Hi!
Over several months I have noticed that the volume for my microphone changes after reboots.
Can someone explain my why this is happening?

17 days later

I also noticed that it no longer keeps my last selected sound device on reboots. Happens for output device.

No, he's talking about input not output. Says it in the title...and the fact he says microphone.

Simply put, the settings for microphones are not saved. May be due to pulse audio or something in the software chain is something wrong. Maybe a bug?

That's the case with my laptop too. When I turn on or reboot is always the micro and bluetooth turned on or enabled. I always have to disable it. Until next time. Ergo. The settings will not be saved.
Whether that is due to solus itself I believe less. Rather not.