Developers of Proxifier told me the reason and gave me a solution.
Thanks for the info. We have reproduced this issue. Apparently, wsl.exe displays this error if Winsock LSP DLL gets loaded into its process. The easiest solution is to use WSCSetApplicationCategory WinAPI call for wsl.exe to prevent this. Under the hood the call creates an entry for wsl.exe at HKEY_LOCAL_MACHINE\SYSTEM\CurrentControlSet\Services\WinSock2\Parameters\AppId_Catalog This tells Windows not to load LSP DLLs into wsl.exe process. We have a tool that can make this call: www.proxifier.com/tmp/Test20200228/NoLsp.exe Please just run as admin with the full path to wsl.exe as the parameter: NoLsp.exe c:\windows\system32\wsl.exe This has fixed the problem in my case. Please let me know how it works for you.