Export to iTunes / iPhone Sync

I am looking to get a copy of my Lexicon library on my iPhone, so I can listen when I am on the go.

The easiest way would seem to be to export to iTunes / Apple Music on the Desktop and then Sync the Library, which the iPhone should pick up.

I export the Lexicon playlist and import - which goes fine and exactly the right number of tracks get exported. However, these playlist never sync to mobile correctly.

I have an active Apple Music subscription and iTunes Match - which is enabled.

The playists appear on the iPhone - but most have between zero and three tracks, where the Desktop version has 50/60+ each.

I realize this isn’t a Lexicon but an Apple Music issue - but would be great to understand if anyone has solved this - or found another good way to have their library on the iPhone including the folder/playlist structure.