InDesign 15.0.2 slow PDF creation, gets worse the more PDF's i shoot in a row, finally indesign quits.

It all started when indesign was working very slowly.
I fixed this issue by turning off GPU and Preflight.

I have to regularly shoot Hi and Lo res PDF's, 50 at a time, 2 page brochures, 100 pages in the document, the first 3-5 pdf's shoot fine, then it starts to slow down, i spend 30 seconds on each pdf just watching the spinning progress wheel before it will even let me type in the page numbers, this gets worse and worse until Indesign quits.

I have recently paid to have a new 2TB SSD drive fitted and upgraded to Mojave 10.14.6, this has made no difference, i have also removed external backup drive, again made no difference.

One of your engineers actually told me that 30 second wait is perfectly norman!!!!!! Having used Indesign since it first came on the market i know this to be rubbish. I never had similar problems with CS6, CS6 created PDF's almost instantly. This is very frustrating and has slowed my workflow down to about 1/3.