Unable to open video device - RTSP stream works on other software

Hi, I've got MotionEye (motioneye:master-amd64) running on Docker on top of Linux Mint Lubuntu 20.04. For the camera, I've got a generic surveillance camera streaming under RTSP protocol. Since a few days past, MotionEye will just display a grey picture with a laconic "Unable to open video device" error message. Trying to set up the camera once again only gives the error message "Connection reset by peer". The streaming works just fine on ONVIF device manager under Windows 10, so I can exclude a connection issue. The only workaround is to change the RTSP port on the camera settings, then it will start working again for 24 hours or so before giving the same error. What am I looking at? What log files should I be checking?