Phone link error 256 with S22 Ultra

I have had Phone link working for years with my Samsung Galaxy S22 ultra.

Recently, part of the functionality stopped working, specifically, the "open phone screen" part. I keep getting an error 256.

The phone is on Wifi, connected to a Ubiquiti NanoHD.

The PC is a desktop on 10 Gbps ethernet.

Both are in the same /24 subnet, using DHCP with IP reservations in the router.

The phone says it's connected to the PC. The PC says the phone is connected to it.

I can see the phone's text messages & photos on the PC.

I just can't open the phone screen on my PC, or show any app on my PC's screen.