Dropping your bobbin case can cause damage. There is a tiny little check spring in there that could have popped out.
Problems on the bottom are usually due to top tension however, yesterday, I inserted a new, plastic prewound bobbin which I knew was over-full for my machine and my top thread looked ok but the bottom was all loopy and railroad tracks and the top thread was just laying on top. So, I pulled off a few yards of the bobbin thread & re-inserted. Now it sews fine. I know better than to put this batch of prewound bobbins in without pulling some off first but I did it anyway.
Back to your problem. You said you did the bobbin drop test and it hit the floor. How fast did it unspool before it hit the floor? It's only supposed to drop slowly and with some threads, you have to shake it a little to get it to drop.
If adjusting the little screw on the bobbin case doesn't change anything, then I believe you have knocked the tiny little tension spring out of whack. Having an extra or even a couple extra bobbin cases on hand is a good thing. That way, if you use more than one kind of bobbin thread, you can have each one individually adjusted for each type of thread.