big pdf export problems


I'm having major problems trying to export a 48 page A5 document  to pdff in the new CDGS 2018. I've been exporting these documents (a monthly News booklet) for years in X5, X6 and X8 with no difficulty whatsoever. The first time I tried to publish to PDF in 2018 it only exported 4 pages out of 48, I checked all the settings and again the same failure. 

I saved the document to X8, opened it in that version and exported it to pdf without issue. Same settings.

I've repaired 2018 and even uninstalled and reinstalled (from the disc). Same problem. 

Can somebody please help.

Thanks, Colin