I wrote to chromium developers, so, here is the summary

It is not a crash, it is a failed debug assertion It happens if: you use webview's chromium backend (recent versions, old versions don't have this assertion) some part of you code consumes COM and that code's thread is not explicitly initializing COM via CoInitialize or CoInitializeEx

My code uses a library that was not properly initializing COM in its threads before calling CoCreateInstance. Calling CoInitialize should fix my issue, but I cannot prove it until I have access to that libraries source code.

What is left to be done by qt/webview team is to fix the failed assertion on "Chrome_InProcGpuThread" which is not created by user.