My first suggestion would be to reflash the ROUTER firmware RutOS using the ‘Bootloader’ process, then follow the instructions to generate your certificate, as per my previous post.
If your RUTX50 has the Quectel RG520N-EU Modem AND you have upgraded the MODEM firmware to version RG520NEBDCR03A05M4G, then it appears that this version is causing any number of problems. Teltonika are working on finding a solution, although there is a possibility that it is not related to your issue. Here, you can find one of the many differing posts on the new MODEM firmware, which includes a fix (firmware downgrade), that will require a certain level of competence.