Corporate networks (especially those utilizing MITM) block vpn access altogether.
You can't reach your vpn server, falling back to plain un-tunneled https. Then instead of dns retuning the true ip, it returns a local corporate ip; you connect to that with https and it serves you a cert generated on the fly for that particular domain signed by a root cert your browser already trusts. Your browser sees nothing wrong and transmits via that compromised connection.
You can usually check for this by connecting via mobile data, taking a screenshot of the cert details, then doing the same on work wifi and compare.
If the cert details change on wifi, your traffic is being intercepted, decrypted, read/logged, then re-encrypted and passed to the server you're trying to reach.