How import the crates ???
I had the same problem. After a long nightmare I found the solution: “Simply” put all your crates in Serato to the first level without any substructure (yes it is a nightmare) and then all the creates will show up in Engine Prime.
But I want to pass them as they are and not to change the whole layout of the crates …!
Kind of moot for me as I use Smart Crates. Hopefully Smart Crates are coming soon to Prime