I tried out PHH SU (which didn't want to install) and the addon-SU from LOS was kinda broken (I accidentally disabled dev options and then I could no longer access SU permissions or disable or enable it). Either way, I went back to magisk, which somehow doesn't have issues anymore.
Regarding my sound issues, when I flashed magisk I always had media issues: gboard would not make any sounds when typing, youtube would load videos really slowly and then media volume would be disregarded. I wasn't able to change media volume and while in that playback session it would stay at the one it was when the video started.
After this, I uninstalled Magisk completely through the included interface, and didn't have any issues anymore. After trying out anything other than SuperSU, I went back to Magisk and I don't have issues with it. Before, the problems described earlier would occur on every boot, but now I cannot reproduce it anymore.
The UI was also smoother when running unrooted/LOS addon, and I can't understand why. If they happen again, I'll take a logcat.