This is just knowledge sharing in case it can help anyone else.
After upgrading from 8.0 to 8.1 and then installing SSL certs from a CA, I was unable to open a designer session (gateway and client sessions were OK). The designer was giving a message like “missing or invalid SSL Certificates”.
The fix was to uninstall the designer launcher, download a new one from the gateway, then reinstall. After that when attempting to open the project for the first time you’re asked whether or not you want to trust that certificate. Once you accept the certificate you can then open the designer normally.
Hopefully it can help someone.