

In that case, something is invalidating the login. Are you sure that it is happening due to leaving your LAN, and not just coinciding with that?
Does restarting the laptop log you out, or temporarily disconnecting from the internet? Could you test by switching to a wifi hotspot on your phone, and switching back, for example?
The client stores your session token in the OS credentials manager (kwallet for linux kde, for example) and the issue can lie there, as well.







With nextcloud in particular, nextcloud is not just nextcloud.
It’s a bunch of additional optional services that may or may not work as-is on Synology. And the Synology package won’t come with all of them.
With docker, adding (or removing) additional services, such as Nextcloud Office, is comparatively simple.