To start, please update your device to the latest RUT_2_R_00.07.04.1 firmware version, with Keep settings option disabled.
If the issue persists afterwards, 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 insight into the issue.
Attached files are private and visible only to Teltonika Moderators.