UPDATE: Now that I'm back home & can now look into this issue in more detail, turns out that I'd been signed out (server side) from Tailscale again. Once I re-authenticated and tested out remote access, everything worked as it should. I remember having to do this several times before, so my question then became "Why am I having to re-authenticate Tailscale again?"
I saw a post that suggested disabling "key expiry" (apparently less secure, but willing to so if it prevents having to re-authenticate Tailscale). So I did. Maybe that'll help.
End UPDATE
My remote access via Tailscale experience has been inconsistent at best. For me, it has yet to be a smooth/user friendly experience.
I'm currently away from home (out of town) and (once again) my server "could not be discovered" when opening Channels app on Android. I follow the process to "Connect to Channels DVR/At Home" as directed, enter the the Tailscale IP address associated with my Channels server, and continuously get the "Channels DVR server not found at..." error message.
My server is set up for remote access. I'm on a secure network. I tried reauthenticating Tailscale, cleared cache/data from Channels DVR app, turned Tailscale off & on - basically, everything I can think of at the moment.
Not sure what more I can do (remotely) until I get home.
Personal rant (my apologies in advance):
I don't use the Tailscale/remote access feature very often, but when I do (like now) it seems to be 50/50 on whether it'll work. The (old) port forwarding method always seemed to work well.
End of rant. Again, my apologies
