Engine prime as a piece of software is great at reading lots of different types of files. It’s File support abilities match any of the Prime SC, Go and Prime 2 / Prime 2 models
The 8000 isn’t completely a prime model, and doesn’t support all the file types that engine prime software does. Especially things like variable bit rate - also I think the 8000 is still touchy about oversized album art and odd characters in tags - you could try deleting the tags on the problem files and re-typing them if all the bit rates and sample frequencies look ok
So, you can have audio files which engine prime supports, which the 8000 doesn’t support