Garbled display forerunner 965

Hi,

My watch at random switches off the display completely. Interestingly, I can hear the functions still going, like the lap timing. It can also give a completly garbled display like the one below. It seems to be temporary; after 30 or 40 min it all off a sudden switches in normal mode as if nothing has happened.

I do have the latest software, version 23.20.

Any ideas are much appreciated.

Bas