Hmmm. Try cycling iMessage off, restart the phone, then enable iMessage again.
If it is still giving you issues, it could be some networking issue. Some things to check: Reset network settings on the phone. Make sure you are not on a VPN. Turn off Private Relay if you have it. Make sure your router/modem isn’t double NAT. Just try to eliminate anything that complicates the network. If it fixes it, then add the complications back one at a time until you find what caused it.
Definitely file a feedback report.