OK, i’ve been frigging around for several hours here. Changes made to id3 fields (Comment, remixer, etc) in Lexicon will sync to Serato.
When I generate cue points in Lexicon, they DO NOT sync to Serato.
I had this working earlier today, then… nope.
Updated both software. Reinstalled both software. Nope. several hours later I’m out of ideas. Issue is likely between monitor and chair but WTF is going on?! 
Serato DJ Pro 3.2.1 (same issue with 3.1.16), Lexicon 1.7.0, Windows 10, frustrated user (likely issue) [who was meant to be playing tunes tonight not fu**ing around with software!]
What kind of cues are you doing? There is one thing to note which is that deleting all cues and trying to sync that to Serato, will not work. Any other amount of cues should work. Reason is that this is a safeguard to prevent new users from accidentally deleting all their cues.
Otherwise, it could be that your files have double ID3 tags which technically makes the ID3 tags invalid. Lexicon may be writing to one of the sets of ID3 cue tags and Serato may read the other.
Hi Christiaan, many thanks for your prompt reply!
I was trying to apply cue points to tracks that had been previously analysed in Serato, but did not have any cue points. I’m understanding your first point as - you cannot use Lexicon to delete existing cue points and sync that change back to Serato?
I think your suggestion about the ID3 tags is the answer - I made some changes to the ‘remixer’ and ‘comment’ fields in Lexicon - these did sync to Serato, but when i check in MP3Tag these fields are not updated. MP3Tag is setting all tags as ID3v2.3, when I changed tags in Lexicon and ‘write tags to file’ the tag changes to ID3v2.4 and changes are visible in MP3Tag, it also resolved the cue point syncing! I do need to re-scan ID3 tags in Serato to se the changes.
I’m really not sure what the issue was exactly, but its working as expected now. THANKS!!
Okay cool! Yeah ID3 tags are a wild west so sadly these random things can happen 