Anyone have an explanation of why bearing sometimes goes responsive, but when I flick it, I still spins like there’s no problems?
Its called a “break in period” it is just the lube that the manufacturer originally put on wearing down.
So just grin and bear it?
Help?
Could be a piece of debris in there. When there’s no load, it’s just hopping around on the inside of the bearing. Under load it might be getting stuck between a bearing and the outer race.
All I can suggest is cleaning it.
My kingdom for a bearing that is fully sealed, doesn’t have the potential to create its own debris inside (balls or race having particles come off) and doesn’t require cleaning. 
First thing I’d recommend is checking both bearing seats for debris. The bearing could be rubbing up against it while put together, slowing down the bearing.
If after giving the bearing seats a good wipe down the yoyo still plays responsive, try cleaning the bearing.
If that doesn’t work, it’s probably a response issue. If the response is new, you probably just have to break the pads in. If it’s old, it’s probably time for a new set of pads.
Just clean the bearing and lube it.