Going to add on here - the sounds sticking gets much better as you learn more kanji and more Japanese because the types of sound combinations that are frequent/likely are more salient in your brain. E.g. after many kanji that sound like ‘しょう’, it’s easier to associate that sound with a new kanji because you’re more used to that being a sound that goes with kanji. At least, that’s what I’ve found as I progress. It can definitely happen at the start that all of the sounds feel random and not at all like words or word parts. I found things sticking better as my vocabulary of Japanese words that I had heard/learned grew a bit so I had a better feeling for common sounds.
I also found on early levels I needed to study more to get things to stick - I did writing things down during lessons a lot more then - again, I think part of my brain getting better at learning Kanji over time.
Finally, I’m sure you know this, but especially after you first learn an item (or generally when it’s at Apprentice 1), it’s really ideal to hit that 4 hour review interval to help get it to stick a bit better in your brain. If you can’t (because of work, life schedule, whatever), you might want a quick way to review the kanji at that shorter than 12 hour interval - e.g. a flash card for the new words that you look at 1-2 times between the lesson and the first review; a note on your phone with the kanji etc. Some people note that they really need a lesson, 1 hr review, and then the 4 hour review, so review their lessons about an hour after taking them to help things stick. Obviously ability to do this varies based on your life schedule, but it might be helpful.