Microphone is not working when loudspeaker is on

Hi! I have a problem with my m4. The mic seems to turn off when i switch to loudspeaker during a call or if i start a fb messenger call with camera on. However the mic works fine with normal calls, i can record, use google speech etc. Mic test succeeded. Safe mode on and the same thing happens. I have put newest rom for central europe 26.1.A.2.147, wiped all possible data via flashtool and even on clean phone without any apps the problem still exists. I did not change any settings or so. It is just the mic not working when i wany to use loudspeaker ( the onr on the bottom of the phone). I also had issues with lower volume levels than in other m4, but here the rom update might help - i will see in fee days as i did rom update today. Do You have any idea what is wrong? The phone never had contact with water etc.