We bought a TRB140 gateways, it came with fresh firmware - TRB1_R_00.02.06.1, we tried to import our certificates but without success. We didn't get any errors and the certificate just didn't show up in webui, we tried different extensions .crt .cer .pem etc. We generated a lot of certificates, we spent a lot of time on it, we tried different browsers, different physically devices etc.
We imported the older firmware TRB14X_R_00.02.04.1, then we imported the certificate without any problems. Later we re-uploaded firmware TRB1_R_00.02.06.1 with the keep settings options and we can now see the certificates in the certificate manager.
I think this is clearly a software problem, we found a solution but it's not convenient.