Just checking, have you seen these?
How to load assets from .pak flies to your game at runtime?
Patching, Content Delivery, and DLC in Unreal Engine | Unreal Engine 5.0 Documentation
How to Create a Patch in Unreal Engine | Unreal Engine 5.0 Documentation
The docs can tell you more about PAKs than I can 
If you have any log file of it that might point at something