i have the same issue.
e.g: i am using obs, i am still in discord. Then I close obs and somehow suddenly the discord crew has another volume.
Also very often my coop mates have to re-adjust my loudness level because sometimes i am super quiet and sometimes i am normal loud. Most of the time after OBS is closed right after the OBS killing Discord somehow fucks up all Audio volumes.
At this point we are started to making fun on Discord and i guess the Problem isn't OBS - it is discord?
Discord really seams to mess around with your system audio devices.
Two Years before i had problems when i started OBS AFTER discord my OBS did not recorded my audio (even if i had visible outputs in the obs mixer the record did not recorded audio) It took me ages to understand that Discord was the problem.
So every time i recorded in the past, i made sure that discord was closed or if i needed it, it was started after OBS.
But this bug is luckily gone.
I will switch over to Teamspeak again because the Quality of Discord gets worse and worse.
I Often have to switch the Discord Servers because often during a voice session everyone starts to sound like mf robots xD
first time it was funny... but i guess its time to move on ^^
Sorry for the long story - in my opinion its some fight between OBS wants to take over to the audio devices and as well Discord also wants, too - Catfight time