Hello there @WiseSplinteR!
Checking around the community, and reviewing your log, I believe the line we are looking for is this one:
UATHelper: Packaging (Windows): LogOutputDevice: Error: Ensure condition failed: FunctionNameFName != FName() [File:D:\build++UE5\Sync\Engine\Source\Editor\Kismet\Private\BlueprintCompilationManager.cpp] [Line: 2759]
The error suggests that one of your blueprint functions is not reaching a valid target. As a first step, test by refreshing your nodes, and recompiling all your blueprints. Next, use “Fix Up Redirectors” to check for any possible wrong calls.
If the issue persists, then we would need to pinpoint which blueprint is triggering the issue. As a test, make a backup of your project, then use the copy to delete blueprints one by one, following by a pack attempt.