The iOS app shows “Router unreachable” with the expired SSL message as the reason, but when I go to the web interface from my computer and check for a firmware update, it says “Current version 8.3.0 No update available”.
I am not sure there is a fix other than to upload your own certificate. We also have several such devices where the FW is frozen at 8.3.0 where the certs have timed out. Peplink has indicate it would only update this FW for security issues but apparently does not consider a cert update such an issue. This is indeed unfortunate as we consider Router Utility to be a very valuable tool.
For device that running in 8.3.0 and above, the SSL cert can be set to auto update from IC2. For more information, you can refer to the forum discussion below: