Sorry for the delayed response.
We do not restrict the ticket creation on change of domains for support email addresses. But we would need to check whether the forwarding to support mailbox has been reconfigured to the new mailbox and the new support mail address is activated.
We could also see that you have reached out to support and we were able to help you with the issue by verifying the email headers. To answer your other question, when an agent forwards the Email, Freshservice will create the ticket on behalf of the requester rather creating it for the Agent, this is an intended behaviour when an agent forwards an email.
Hope this helps you.