I would like you to attach a troubleshoot file to your question. Please, replicate the issue, 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 details in to the causes of the issue.
Attached files are private and visible only to Teltonika Moderators.
I would also suggest to consider updating to the latest firmware version, preferably, with Keep settings option disabled. Be aware that this will delete your current configuration.