I've had the same problem today, but I've been looking at WSJT-X as the source of the problem, with no success, as Grid tracker stopped working too. Its like WSJT-X multicast has stopped working.
Last night I turned off the laptop with everything work. This morning, on a fresh boot up, I installed JTalert 2.50.2 along with .NET runtime 5.0.7. From then JTalert started complaining that it cant communicate with WSJT-X.
I then tried launching Grid tracker (I cant remember when I last used it, but was already setup for multicast) and it has a similar problem. I then uninstalled JTalert and .NET and it still didn't fix the issue with Grid Tracker. I then installed WSJT-X v2.5.0 rc-1 but got the same issue.
So I started adjusting the IP addresses and ports in the WSJT-X config with no success.
Going back to unicast (127.0.0.1) with individual port number per WSJT-X instance allowed Grid Tracker to communicate with each instance when I set the correct port number in Grid Tracker, but JTalert is displaying the same error regardless if its unicast or multicast. The error is showing that its detecting the correct port and IP address to listen to from the WSJT-X config but no traffic is being passed in either unicast or mullticast mode for JTalert. Grid Tracker on working in unicast.
Below is sample Jtalert error when trying to use multicast:
Unable to communicate with the WSJT-X process.
UDP Port : 2237
IP Address : 184.108.40.206
Values read from WSJT-X config file...
C:\Users\chris\AppData\Local\WSJT-X - SliceB\WSJT-X - SliceB.ini
WSJT-X Detected Instance...
Process Window Title : WSJT-X - SliceB v2.5.0-rc1 by K1JT, G4WJS, K9AN, and IV3NWV
Process Command Line : "C:\Radio\wsjtx\bin\wsjtx.exe" --rig-name=SliceB
Decode alerts and logging will be unavailable until corrected.
I've also tried disabling the Windows Firewall, deleting the entries in the firewall rule set for JTalert and WSJT-X but no success so far.