Nextcloud 13.0.6: Desktop client does not work with linuxmint 19.1

Hi, I tried to run our Nextcloud 13.0.6 with brand new Linuxmint 19.1 and have troubles: It does not seem to install proplerly.

  1. It asks me to admit access with username and password
  2. I choose the right folder to synchronize with
  3. nothing!
  4. I restart nextcloud descktop client
  5. it tells me that I have been logged out
  6. I start nextcloud desktop client again
  7. back to step 1
  8. never ending loop.

Has any body advice?
Thank you!