Yeah I've had a similar issue with the Anki-like system Wanikani uses for learning Japanese Kanji. I can keep up for some time, but as soon as I get busy with something else, I get overwhelmed by the piling up reviews. It has been very effective for the ones I learned when I was able to keep up though.

Recently a friend got me into Duolingo with him, I've been managing to maintain a streak on it because if I'm too busy I can atleast just do a quick "lesson" before midnight, but I don't really find it to be very effective for learning unless you're coming from literally zero starting knowledge.

I already know the basic vocabulary (especially phonetically) and sentence structure, so it's too slow. I usually just do the first handful of lessons and have figured out the kanji enough to just jump ahead to the test to unlock the next unit.