Hello,
For starters, 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 insight into the issue.
One thing to consider is a firmware update to official Teltonika version. You will probably not be able to update straight to RUT2_R_00.07.0 and above, or at all, depending on the product code of your device, thus try RUT9XX_R_00.06.09.2.
Be aware that since IT007 and RUT9XX firmware versions are different, device will probably not pass 06.09.2 firmware validation and will require to install only a fresh copy of the firmware with the previous configuration reset to default values in order to prevent the device from bricking.
Best regards,