Audio and app problems?

[Plushybunny]

Plan

Premium

Country

Germany

Device

OnePlus 7 Pro

Operating System

Oxygen OS10

My Question or Issue

Two things:

1.: Since some days, Spotify's volume is EXTREMELY faint, when I use the app in my car on aux. What happened? Did I accidentally change some settings?

2.: Also since some days, I don't see the volume bar in the app anymore. I can only change the volume by changing it via the hardware. Which is definitely not optimal. Where's that gone? Again: My mistake?