Haven’t tried 4.25 yet, but as of 4.24, what you are seeing is fairly typical in my experience so far. I personally have issues with any parts in the assembly that are constrained to any odd angle, other than 90, 180, etc. I’ve been importing those parts in 3dsMax and going to UE4 that way.
Some parts I just can’t import at all. No error message, just creates a dummy actor and no geometry. Haven’t figured out what exactly causes it.
Datasmith used to crash when importing an assembly with an LOD view enabled in previous versions, so I got in the habit of leaving the master LOD open before importing. Not sure how that stuff is currently handled to be honest.
This is using Inventor 2020 btw. I’ve never had an issue with new inventor versions and datasmith, but I don’t keep old versions installed so I don’t know how older inventor versions work with newer datasmith versions.
Sorry its not much help, but you’re most likely not doing anything wrong.