Problem
After installing the July 11, 2023—KB5028169 (OS Build 14393.6085) on a Windows Server 2016 hosting the K2 application server, the 'K2' Classic Application Pool used to host the legacy K2 API endpoints may crash when accessing the [K2 URL]\/K2Services/WCF.svc endpoint.
Solution
The issue appears to be directly related to Microsoft July 11, 2023 — KB5028169. Uninstalling the update or installing the newer August 8, 2023—KB5029242 (OS Build 14393.6167) instead will resolve/avoid this issue.