Hi Frode,
Clarifying question, did you reset the Zigbee network after upgrading to the experimental Homey v5 release? Indicating that you still have them included, I guess not.
Unfortunately, the migration from v4.2 to v5 is not stable and might indeed lead to non-responsive devices. Only solution for now, would (unfortunately) be to reset the Zigbee network, re-add the devices and rebuild the flows. Sorry 
