Messages.app on macOS won't send/receive/display messages to/from one specific contact I have a strange situation that I can't puzzle out. There is one particular contact that I can't send or receive messages from in Messages.app on macOS 10.15.7 on a MacBook Pro. I can receive and send messages with this contact normally in Messages on my iPhone (although they don't appear on the MacBook Pro), and I'm having no issues with any other contacts in Messages on either the MacBook Pro or on the iPhone.
I've tried a few things to no avail:

Restart Messages. No effect.
Restart the computer. No effect.
Delete the phone number from the contact and tried to send to the plain number. No effect; it still acts like it's associated to the contact in Messages.

Not sure what else to do here, as most potential solutions that I come across are about what to do when Messages isn't sending to anyone, not just one particular contact.
How to fix?
This post solved the issue. On your iPhone:

Open Settings.
Scroll down to Messages.
Tap on Message Forwarding.
Ensure that all the devices are selected.

I just switched from my old MacBook Pro to a new one, and I didn't even think that I'd need to do something like this.  Still not sure why it affected just this one user, but after doing this, the problem was resolved.