Hello Kinnetiklax,
Since this happens with a specific network, try the guidance from If your Mac doesn't connect to the Internet over Wi-Fi.
You might also be able to find and review the certificate by doing the following:
"Trust a certificate on Mac
- In the Verify Certificate dialog, click Show Certificate.
- Review the certificate, then if you have confidence in the server or signature, select the checkbox to always trust the certificate or to acknowledge the signature is valid.
To read about current trust policies, click the arrow next to Details. See Change Certificate trust policies.
3. Click Connect or OK, then enter your account password (if required).
If the certificate is a root certificate, enter the name and password of an administrator of the Mac you’re using."
Take care.