@roxd, My workaround was to mount the writable partition on a different Linux machine. There I was able to manually append the missing SSH public key(s) to /writable/user-data/username/.ssh/authorized_keys.
This worked on a WDLabs Nextcloud Box running Ubuntu Core 16 and Nextcloud 11.
@roxd, My workaround was to mount the writable partition on a different Linux machine. There I was able to manually append the missing SSH public key(s) to /writable/ user-data/ username/ .ssh/authorized _keys.
This worked on a WDLabs Nextcloud Box running Ubuntu Core 16 and Nextcloud 11.