can't control volume of a bluetooth speaker after update to Sonoma 14.4

so after the update to Sonoma 14.4 (on macbook m1 pro) the bluetooth speaker cannot be controlled by neither volume +/- keys nor via sound system settings with mouse. I have several BT devices connected, they all work fine (BT mouse and keyboard).

The BT speaker works, connects fine, but pressing volume buttons on macbook only enables it to quite a loud setting or disables it completely. The volume bar moves, but doesn't do anything in terms of sound volume. Volume keys work fine with the macbook speakers and BT headphones, so it's an issues with only this device.

I tested the speaker with a Windows machine and an Android phone and the volume can be changed just fine from them, so something went wrong with the Mac OS I believe.

I tried some methods suggested in forums (sudo killing bluetooth, restarting, "forgetting" and reconnecting the speaker, deleted com.apple.bluetooth.plst file and restarting), but nothing helps.

I'd appreciate if anyone could help fix this...