Can’t think of a good mnemonic so you make up a dumb mnemonic.
Example: YO (よう), the SUNSHINE feels good on my face!
Do your review and you cannot remember the reading for the life of you.
Go back and think of a better mnemonic.
Example: The SUNSHINE is warm and yellow, like an egg YOlk. (よう)
Do your review and can only remember the first (dumb) mnemonic.
Whatever works I guess ¯_(ツ)_/¯
Well, this for sure happens to everyone.
Since lvl 10 I started doing my own mnemonics, I liked short sentences made by wanikani, but then they became a wall of text and I remember the story but not the reading/meaning. So had to create my own.
Completely normal phenomenon. I usually have to do more 2 or 3 lessons with that item to finally starting to remember it.
Since I created it in the first place, I didnt need to go back and create a new one.
Same as 3.
The way I see it, at least in my experience so far, the most memorable mnemonic has been the most effective in helping me remember, no matter how weird or how dumb it is, not necessarily the nicest mnemonics.
I don’t want to take too much time creating a nice-sounding mnemonic. I’d rather have one that helps me remember the meaning and reading of the kanji most effectively.
Yes, 1 & 2 is how it usually goes for me. I try to find some word or expression in English that sounds like the reading AND has a meaning that I can relate to the term, as in “west SIDE” (西/さい). But occasionally if I can’t find a meaning connection, I’ll just make up a sentence that uses the reading as an interjection (as in, “Yo, make a plan beforehand (予/よ)” or “SAY, it sure is quiet in here” (静/ せい). I find that this latter strategy is not as effective because there’s no real meaning link between the mnemonic and the term. Which is why I find it funny when I somehow remember it anyway. 
Maybe make an exception for the late-and-mostly-not-lamented “Jourm”, though… 