I have a subset of Windows 2019 Server OS systems that when patched with the October MS patches will consistently display black boxes where the application window are. I am still attempting to determine what the exact configuration needed for this is though. Removing the October MS CU does not resolve the issue. Servers are running 2507 CU2. What makes it diabolical is that it does not happen to all servers equally. I have a large dataset of 2019 servers that are patched with October patches that work perfectly normal, but a few that are broken when the patch is installed. If anybody else runs across this and figures it out, I'd appreciate your findings. I have a ticket open with Citrix as well and they weren't able to find anything in the logs that led them to a quick fix. The AOT logs show the error in the image, but aren't super helpful either.

Following this because I have a few complaints of black boxes again as well. Haven't had time to dive in yet.

Found the fix and somewhat the cause, though very odd. Somehow during the patching the 64-bit VC Redistributable .dll files reverted to quite old versions. Uninstalling the patches naturally did not fix the .dll files. A quick reinstall of the VC-redist.x64.exe and a reboot things were all back on track again. support.citrix.com/external/article/CTX695909/citrix-virtual-apps-and-desktops… Though not the same symptom we found the above article helpful in finding the solution.