Had this same issue awhile back, are you in Tournament mode by chance? If so turn it off there is a bug that causes this problem. If I recall correctly if you lock both balls on the same ball without draining is when this issue comes up if you lock one ball, drain and then lock the next it works ok. It could be vise-versa but you get the idea. But I'm 99% sure it's the tournament mode being on.

I'm not sure on that but I believe L-6 is the most up to date version and it is on that one for sure.

Ok, well I do have the patched ghosting rom, thought it was L-6, but either way the bug is on that version too.

Yeah I had my game trouble free for years and had set mine to tournament mode once I joined s league and was supposed to host in the future, it was after that when I started having the exact same issue and was going nuts trying to figure it out for awhile.