Hello,
UE uses a dll file in your Alias application to read the wire file.
The crash you see, in your second message, is that your 5.4 install is trying to use Alias 2025 and fails because of compatibility issue. The crash itself should be handled better but, anyway, in that situation your wire import would fail.
Now, what I see in your first message is that you also have a crash with UE 5.5. This is a bug we would like to fix but will be tricky as we did not reproduce it with our test files yet.
Regarding your 800K actors import, once interchange CAD is production ready you will have more options to simplify product tree on import. But even that might not be the solution if you still end with hundreds of thousands of actors. The solution of importing and processing several sub assemblies individually will always remain less taxing on the engine and computer ressources than your full catproduct.