Hello,
Have you tried if this issue is present on RUTX_R_00.07.02.7 firmware?
Does this happen only with your generated certificates, or are you not able to upload any certificates at all?
Also, if possible, could you attach to your question any dummy certificates, which could temporarily used for testing, without compromising your security?
Lastly, I would like you to attach a troubleshoot file to your question to see if the logs show any issues. Please, replicate the issue, then access router's WebUI, go to System -> Administration -> Troubleshoot section and download troubleshoot file from there.
Best regards,