Lenovo miix 320 cameras not working

Hi,
I am new here!
I have been using Ubuntu Mate happily since a number of years on a now very old eeePC 1005HA. Because of the limitations of the 32 bit hardware I recently changed to a Lenovo miix 320 convertible with 128 GB SSD. After some initial glitches almost everything is now working fine with mate 18.04 on this hardware except from the two cameras (front and rear) that are not being recognized. I have been searching desperately in various forums but so far I could not find any way of making these cameras function. I am also regularly updating the system in the hope that this would be overcome. So far in vain. Does anybody know of drivers, modules, or whatever to make these cameras work under ubuntu mate? Maybe a downgrade to 16.04 would help?
Thanks for hints, D-E