If after upgrading a Digi TransPort® router to release 7.1.x.x or later and it loses connectivity via HTTPS, this is due to new security measures in the newer firmware releases.
The old certificate was seen as a security risk as it was exactly the same in all Digi TransPort devices. The new firmware will now detect the old, common certificate, and delete the certificate file when present. Once the file is deleted, the Digi TransPort will generate a new unique, self-signed certificate to replace the common one.
However, before the Digi TransPort can generate the new certificate file, it will need its system time to be set to the current time, either manually or using S/NTP. If it does not have current time established, the certificate will not be generated, preventing HTTPS from working on the router until time is properly set.
Note that this issue does not affect access via HTTP, which does not use certificates. You will be able to access the WebUI using HTTP if it was enabled before the upgrade.
Feb 10, 2020