Yeah, I honestly don’t bother with learning how to write them, as I don’t think it’ll ever find a use for hand-writing Japanese… But I heard it helps some people with retention, and it’s a cool skill to have! 
Grammar for sure. But another pitfall of mine are words written out in kana… The kanji hold the entire meaning and reading of a word for me. When I see it written out in kana, even when it’s a word I could have enlightened or burned, I’m like “huh? what’s this word mean? oh… it was that word I obviously know by heart…” It’s really demotivating, tbh…
Generally, I think I struggle the most with applying my learning. I’m pretty solid with memorization, which means that I can pick up new vocabulary and grammar faster with only small amounts of repetition (so far, my WK accuracy has held roughly at a 94%). I never can seem to find time to try and practice my reading, speaking, or listening, though. I’ll always derail if I go into a sentence and can’t comprehend either a specific word or grammar particle. I just go and look up the word and assume I have to hit the SRS grind again so I can properly read that specific sentence in who-knows-how-long. I think if I relied less on translating every little thing then I would learn a lot more from reading practice.
This is actually very hard, because due to the fact that nearly all of the grammar points of a sentence are written in hiragana, when “regular” words (like nouns, verbs, adjectives) are written in the same script, the sentence can become extremely difficult to parse. The English equivalent would be something like this: “Itsliketryingtoreadasentencelikethisitspossiblebutveryhardespeciallywhenthesentencegetsreallylong!” You might have been able to read the previous sentence, but you were probably slowed down a little. Let’s make things even worse:
“Asyndetonhamartiaepizeuxisenjambmentcircumlocution.” That was a long string of words that actually exist! But that sentence was probably impossible to parse, because you’re not familiar with these words. That’s what’s happening when you see kanji written with kana. You know that 花 is flower and is pronounced はな, but you’re not familiar with はな being used all the time. The reason why the first sentence I used as an example was readable, was because your brain is used to the shape of the word, as well as the meaning. This is due to training and reading over many years. When it comes to kanji, you learned to read the shape/character, so when you have to read the same word with a different shape, it’s hard. Does this all make sense? 
TL; Dr: don’t feel bad, this is normal!
I can definitely relate to this too. I held off on doing any sort of reading outside of example sentences because of this. The best thing you can do in this situation, is to actually stop translating every little thing you come by. Don’t understand a word? Skip it. Don’t understand why a certain grammar is being used? Skip that too. You can always go back, don’t worry. When you spend forever trying to look something up, it really hurts your reading flow. Once you reach the point where you spend more time looking stuff up then actually reading, you’ll probably not want to read anymore! And then, at the end of the day, you didn’t get to practice! What’s important, is that your brain gets to pick up the stuff it does understand. The more you do this, the more your brain will get used to catching up pieces of the sentence that it understands, and the more you learn, the more your brain will be able to process. One day, you’ll get the whole sentence. Whether that day is tomorrow or a year from now, it doesn’t matter.
Also, the stuff you learn outside of the SRS programs is just as important. I still remember the word 軸 (じく, meaning axis) from reading the settings for a video game over a year ago. And that was the only time I ever saw the word! Don’t rely on your SRS programs for everything, that’s no fun! 
Much sense, yes, thank you. How to circumvent, though? Anki deck, with かな>漢字 cards?
I mean, you could do something like that, I know Memrise has a lot of decks like that, but the question is, do you need to? I’d say 90% of the time, stuff will always be written with kanji like normal, so I’m not sure you should invest time in doing that when you could be studying something else!
Well… I was just checking out a Japan only title for the SNES, and no kanji existed in the entire game… Considering this is one of my uses for the language, it’s a bit important.
Ahh, I hadn’t considered retro games, sorry! If I can recall correctly, kanji wasn’t used in a lot of SNES-era games. In that case, you should probably give one of those decks a try. I think your brain will gradually get better at reading kana-only words after a while, as long as you keep practicing! It’s kind of like how you can train your brain to read text backwards or upside down: the required knowledge is already there, you just have to train your brain to process it differently. You should get the hang of it the more you play!
I rarely forget my radicals while doing Wanikani or reading, and when I can’t get my head around a Kanji, breaking it down into radicals helps a lot.
But when it comes to physically writing kanji… It’s like I’ve never even seen the language before. Whyyy brain 
I majorly relate with the grammar; especially long sentences, I just start to get really confused. My absolute weakest area is listening. I could read a long sentence and understand, but if I hear the same sentence I just have no idea. I have a pretty strong visual memory but my auditory memory isn’t the same, so remembering something I haven’t seen is nearly impossible (I’m an artist too, which is figured is related). I’ll accept any recommendations for improving listening!!
Consistency.
Maybe we’re doing things differently, but I find writing it easy. Just copy the Kanji into Jisho and follow the stroke order. Writing Kanji helps me so much more than just eye-balling them. No notes or anything, I just write the kanji/Vocab at least once per review session.
I think the difficult part is writing from memory, not copying.
I’m currently working on trying to improve my listening skill as well! Here’s some things I have found helpful:
Watching Let’s Plays of games on YouTube. This helps because the sentences used by the players are often short, and even when you can’t understand, you can still follow along with what’s on screen. Playing games yourself with JP audio and JP subtitles is also a good tip, of course!
Listening to the podcast JLPT Stories. JLPT Stories is a collection of short stories organized by their grammar level. It’s also fully transcribed, so you can follow along as you read.
Using the app Satori reader. This is a really great app where you listen to short stories as you read along. You can tap on words and grammar points to see their meaning. You have to pay for most of the content, but they still have a lot of free content, which is what I rely on.
Watching anime with Japanese subtitles. Although some of the words used in anime are unusual and can be hard to understand, I’ve generally found that characters in anime speak SIGNIFICANTLY slower than actors in live-action drama, so it’s easier to follow along.
Watching the Nihongo no Mori videos on YouTube. These videos mainly teach N3-N1 grammar in Japanese, so you get to practice while you learn!
Those are the things I do the most to improve my listening comprehension, and it’s helped a lot!! Lately I’ve actually found it easier to listen to the audio than read the Japanese subtitles, which would have been unthinkable for me a few months ago! Whatever method you use, do not, and I repeat, ever use English subtitles while you are trying to practice listening! Seriously, I learned this the hard way! If there is something in, say, an anime episode that your don’t understand, wait until you finish the episode before going back and turning on English subtitles. Also, be prepared to rewatch videos, episodes or replay podcasts A LOT. I’m talking 5+ times here, if need be. It’ll be annoying, but trust me, your brain will thank you!
Hope this helps! 
For me, right now, it is 活用! 
That comes with time. I know that I could write several Kanji/Vocab from memory if I was given the Japanese or the English word.
Yeah me too, but I kind of want to be able to write all of them
I struggle with generally remembering stuff SRS helps a bit, but I usually have to go through a lot of repetitions before anything will stick…
This affects my vocabulary retention a lot… I don’t worry too much about it though, important stuff naturally gets more exposure over time 
It also causes me to always depend on the same old grammar patterns every time I say something, even though sometimes I should know better ways of saying it
Time and knowing the language will help. This is one of those things we can’t really do anything about.