I know I hit walls in my growth as a drummer sometimes. My experience, just say 'fu*k it, who cares, I just want to play drums for the enjoyment, and the experience of being one with the drum (really). The next thing I know, I move past it. It seems that for me, I am my own hurdle & to get over it I need to get over my preconceived ideas, and just let go. It's not that I really don't care about getting better, it is that I must not stress over it and have faith that with time & effort, I'll get better. Getting stressed out about it can make it worse.
It seems to be how our brains work—you let a lot in, then your brain needs to organize stuff, and it tries to make a complete concept. So any new info may not fit into that. You have to let that concept break apart, so you can let new info into your head. Then your mind puts it together in a new way. So you seem to make big leaps forward, small step back, and on and on.

In other words DON'T WORRY. Play drums, have fun, It will pass. Life is change...

Sometimes my body seems to settle in at a tempo working on a certain drum lick or rudiment. Try not to get too focused on the speed you can do something, work on form too. When I find I'm leveling off at a certain BPM for something, I just keep working at that level—or just push it slightly. After a while I can move it faster..... just keep practicing.

I think what it is is that your body & mind have to fully absorb being able to do something. Then they can bring in new info & improved technique. Soon you'll suddenly be improving dramatically. Then once again, that stops, and you can't go any faster.... but keep it up & then BAM! Again you're increasing the speed... I always seem to improve in leaps & then lulls— just keep practicing.

I don't ever let it make me think negative — I know it is a process. And I work on a few things at once, so I'm often improving at at least one item, even while other stuff isn't improving... although, sometimes it seems
everything is improving, then nothing is.... that's life.... At times when your
speed isn't really increasing much: FOCUS EVEN MORE ON THE FORM;
your sticking, your hands, the timing—with a metronome of course...
and don't stay too focused on speed. Focus on enjoying drumming.
BE THE DRUM.