I hit 1600 and it went downhill from that

That's normal. Check out this picture:
You are at a plateau. Then you make a progress and hit plateau again. But new plateau is on a higher level than the previous one. And so on.
Same here, but it's dropping to 1500 then 1400 every time I try to climb back up to 1600 bullet. But it isn't stuck there, it's free-falling with no idea how to recover faster to the point I just regret playing bullet and now just want to close my account for my own sake or hide my ratings to stop rage-tilting. Then I try to go for more only to hang pieces left right and center
After quitting chess for about a year or so, I came back to it. I climbed from around 1450-ish to 1600 in a week. However, I am dropping in elo at the moment. I've been stuck in 1500s for weeks and right now I thought I could climb back up, but I dropped below 1500.
During the weeks in between, I picked up chess books, checked out how the London System works, etc. Right now, I'm really frustrated, because I have beaten players at around 1700-1800 at chess.com, but, for some reason, I am struggling with players at my elo.
What are some ways to improve in chess? Why am I stuck at this elo after climbing to 1600? If I happen to get my elo back, how do I prevent getting "stuck" again?