Did I understand correctly that both the base and the rover are shown offline in Emlid Caster, and after restarting, you see them online again? If the receiver is shown offline in the caster, it could be related to the internet connection. Please try another Wi-Fi connection.
If the issue happens again with another Wi-Fi, please share the Full System report, the email address used for the Emlid Caster profile and the name of the mount point. You can send this information privately to support@emlid.com.