Hi Guiseppe,
Thank you for your query.
As far as I understood you meant SSL/TLS certificates by saying protection certificates.
1) Could you please elaborate a little bit how did you test that the transmitting interval can't be longer than 15s? As in general you can select transmitting period freely by navigating to Services -> Data To Server -> Data Senders advanced settings. Try setting the period to more than 15s.
2) What firmware version are you currently using? We have recently had a new firmware release, I would strongly recommend upgrading(if you haven't done that yet) and test when ever the same issue reoccurs.
Link: https://wiki.teltonika-networks.com/view/RUT240_Firmware_Downloads
If, after taking earlier mentioned steps, the issue reoccurs. Please, could you navigate to System -> Administration -> Troubleshoot and download the Troubleshoot file. Forward it to me via Private Message.
Best Regards,
Dziugas