By accident the front panel connector was hit and unit suddenly showed large offset in conjuction with excessive noise.
Nothing can return instrument to normal behaviour (range change, turn off, long time waiting, w/ or w/o battery, etc.), except tapping the connector multiple times until offset is gone.
I optically checked the guts for loose connectors, bad solder joints, suspicious parts, but could not find anything obvious (unit is already recapped).
Any ideas what could cause the issue or where to look at?
To give a better impression of the issue video and pictures attached: