Apologies for the breakage. What’s the callstack at the time of the assertion?
Sounds like a regression may have been introduced in the hotfix if it wasn’t occurring for you in 4.18. Would you be able to confirm if it happens without Blueprint nativization enabled as well? If so, this will be a new issue.
I have posted a new Issue: Assertion failed when cooking content for WindowsServer - Programming & Scripting - Unreal Engine Forums with all the information you requested. However, since I cannot reproduce this using a minimal project, I fear I have to give up on nativization :-(. Thanks for the feedback.
Ah, sorry to hear. Are you able to tell which of your assets are being cooked at the point of failure? I’m wondering if maybe it requires a specific type or asset that currently exists in your project that is not necessarily mirrored in a minimal test project.
There is no logging at this point, but by debugging UE4-EditorCmd I found out that the asset causing this issue was “InvalidLightmapSettings”. Since this is provided by UE4, I followed the hint in the issue I posted to completely rebuild the engine in a different folder (deleting intermediate etc. did not help). With the new engine folder, the Assertion no longer occurs. Sorry for the noise, as this turned out to be not nativization related. From now on I will rebuild UE4 in new folders even for minor releases.