Telephone conversations, sound, and recording are very quiet
If I want to record voice messages in Whatsapp, then the recorded talk is so quiet, that it is very hard to understand. But it is not only a Android behavior, also listen to music or phone calls are very quite, i.e. the sound level seems to be quite low.
Update:The Whatsapp problem is a known issue I realized. " Voice calls with Whatsapp are not usable as the voice volume level is minimal (if can be heard at all)." (https://together.jolla.com/question/208530/release-notes-310-seitseminen/#208530-update-version-history)