Above all, it is totally NORMAL to struggle to remember new kanji the first time you see them!
In my strong opinion you’re kinda missing the main point of any SRS: lots of frequent repetition for items you find difficult and less frequent repetition for items you find easy.
There’s short term memory and long term memory. If your goal is to be able to read Japanese, long term memory is more important, and it depends far less on mnemonics and other tricks and more on sheer repetition. The goal is to eventually recognize items instantly and effortlessly without any tricks.
I often get new kanji incorrect two or three times during lessons and sometimes even for the next several days of reviews. Within a few days, you’ll start remembering your mnemonics and answer correctly more often. Even later you’ll recognize them without relying on mnemonics.
So my advice is to not worry about struggling with lessons. JUST. DO. YOUR. REVIEWS. EVERY. DAY.
If reviews start to become too difficult or your queue becomes too large, slow down on doing lessons.
But lessons are supposed to be difficult. It’s NOT necessary to get your lesson queue down to zero every day, but you REALLY want to get your review queue to zero at least once every single day, and the only way for the SRS to know you’ve found something difficult is if you answer incorrectly, so never feel bad about it — that’s what you’re paying for!
頑張れ!