I run into a similar issue frequently when I reuse a browser tab which contains an outdated/expired session from yesterday.
Try to open a new browser tab and connect to your vCenter using https://<FQDN of your vCSA>/ui/
Good question. Its not clear if we're talking about MyVMware (as in the Web Portal) or if OP is talking about vCenter? I'm assuming the latter, but probably needs clarifying 👍