Just a wee update....
No progress or solution so far more bad news in fact.
I now have a MacPro Intel Dual Processor dohickey pooter otherwise known as a Mactel.
The file that took 11 minutes to open now takes 20 minutes
My Reseller now has a copy of the file and I'm hoping it will be passed onto Graphisoft to have a look at as well but in the meantime I've tried a few scenarios to see if I could find the source or even just find a clue to what is causing the problem.
1 Deleted All the Objects in the file
File size 16.7mb
Time to open file 20mins 30secs (ish)
2 New and Reset and Merge into new file
File size 13.8mb
Time to open file 19mins 39secs
3 Deleted All Details in the file
File size 14.1mb
Time to open file 20mins 30secs (ish)
4 Deleted All Sections and Details in the file
File size 10.8mb
Time to open file 20mins 30secs (ish)
NB the untouched converted file is 17.1mb
Opening the file with no Sections or Details looked momentarily like it was going to open quickly as the progress bar zapped along to almost the end of the progress bar but then just sat there mocking me! (see the screenshot below)
AC versions 3.41 to 25 (UKI Full 5005).
Using AC25 5005 UKI FULL
Mac OSX 10.15.7 (19G2021) Mac Pro-2013 32gbRam AMD FirePro D500 3072 MB graphics