If you ever come across a group in Exchange that you can’t edit, you need to dig out the underlying email address
It’s the mailbox properties, find the mailbox you need, then double click it, then go to the email address section on the menu:
The address you’ll need is the bolded SMTP one.
Then search for that email address in AD. You’ll be able to edit the AD group even if you don’t have permissions for the Exchange one.
The security/distribution group that shows up (and it should as there has to be an AD object in place for it) will probably show a different name – the one from yesterday came up a CSP Team Leaders, but as long as the email address for the group is identical, then it’s the same group as in Exchange.
This happens if the group got created in the on-prem exchange and given a different display name to the email address.