Some visual elements like playback bar and Oscilloscope freeze sometimes

Nobody has claimed this yet.

### Bug Summary
Sometimes seemingly either randomly or _maybe_ after a bit of unuse, some relatively important things visually stop updating, like the playback bar (the gradient that shows up when you play still appears and disappears though), and less importantly things like the master oscilloscope. One time I had this happen I managed to fix it somehow but I don't know/remember how, so generally this forces a program restart. They still work functionally, but they don't visually change at all, which makes them useless. You can still interact with most actual elements in the song editor when this happens, I think.
#### Steps to reproduce
As completely unhelpful this really is, I have no idea. The latest time it happened was when I closed my laptop with LMMS still open, and got back to a while later and it happened. Idk if that's helpful or not, im not sure if the other time it happened even was under the same circumstances
#### Expected behavior
Everything will work properly when I press play/spacebar
#### Actual behavior
Some stuff is completely frozen even if I tri messing with it manually (enabling/disabling osc, ect.).
#### Screenshot
doesn't really work here
#### Affected LMMS versions
I'm on 1.3.0-alpha.1.506+gabe2c92be

Start by reproducing the freeze after closing and reopening the laptop with LMMS still open, then check whether the playback bar and master oscilloscope stop updating while playback remains functional. Compare the visual behavior before and after restarting LMMS; done means these elements continue updating after the triggering scenario without requiring a program restart.

Written by the indexing model from the issue text.