A user can't connect VM by browser ssh with custom port from instance list

User A can’t connect VM (Compute Engine) by browser ssh with custom port from instance list.
But the User A can connct the VM by browser ssh with custom port from instance detail screen.
The user A can connect VM by browser ssh with custom port from instance list too until few days ago. Suddenly this happened.

Also User B and C can connect VM by browser ssh with custom port from both instance list and instance detail screen before/after this problem.

Any hint to resolve this problem?

I must admit that I am lost after the first two phrases…

What you’re trying to achieve here? Not to mention that I don’t get it why would you like a custom port while using the Browser for SSHing into these servers? I mean what’s the point?

I could understand if any of your users didn’t had access to you GCP project and you’ll do it via a sort of port-knocking thingy but why not using the standard ports?!

Anyway, have a look here https://geekflare.com/login-google-cloud-vm/, make sure that your Firewall allows that custom port from IAP (https://cloud.google.com/iap/docs/using-tcp-forwarding) and the VM (sshd service) is configured to listen on that port.

I don’t know why, but time solved the problem. Thanks.