I've not got this issue, but OBS has real bad audio now..
I noticed that the VU meter would peak a lot (too loud), so I turned down my mic in Windows (to 45%), and adjust the 'Desktop Audio' (in OBS) to around 50%, and it was perfect, everyone could hear me & the game fine..
Roll on a good while, I thought I'd stream a bit (I used to do 5 days, 8hours, now I do it when I can be bothered), I have the lastest OBS 19.0.3, opened it up, started streaming with my original settings.. It was terrible, I had to cut my stream from 1080 to 720 (tho it was a fast paced game, so it's typical to have to do that) and I was being told nobody could hear me, so I had to turn up the volume in OBS to 100% again.. When I watched the stream back myself, audio was still way too low..
So I did a couple tests today, 1st I changed the video bits, and bitrates, etc, so I get zero pixelation on 720 now, tho I didn't with the old setting before..
Then I did the audio, so Windows audio out 100%, mic 100%, test stream.. Way too low audio levels, I've now used OBS to boost the desktop audio by +7db, and the mic by +15db..
I really like the software, but whatever you've done to this new version, broke it.. I literaly can't boost my audio any louder from windows, and everyone else complains in the Twitch app, I'm far too loud... Posting a Shadowplay highlight to Facebook, I had to turn the audio down, as it blew my ears off... You've broken it somehow..
I know it's not just me, as a quick google search shows lots & lots of people with the same issue, and being given the same fix, add Gain to the desktop audio, which we really shouldn't have to do..
EDIT: So I re-checked Windows mic audio, and it wasn't saving the chages I'd made to 100%, this time it did, and seems it might be ok in OBS now, I'll check next time I stream.. Desktop Audio is till too low tho, I've had to leave it boosted...