Can you confirm that the connection to 5G itself works?
Which firmware your device has currently installed?
If you have not done it already, could you update to the latest 7.03.3 and check if the issue persists?
Otherwise, I would like you to attach a troubleshoot file to your question. Please, replicate the issue by waiting till the device connects to 5G, then access router's WebUI, go to System -> Administration -> Troubleshoot section and download troubleshoot file from there. The logs in the file might provide more insight into the issue.
Attached files are private and visible only to Teltonika Moderators.