8.4 update crashes on start up

I've updated to v8.4, and the program hangs on start up.

I have spent over 10 working hours on the support chat lines to Adobe so far without resolution of the issue, rolling back to V8.3.1 has allowed me to open all my catalogues successfully.

Issue:

When opening an existing catalogue the program hangs and shows "program not responding" nothing else seems to happen.

Opening a new empty catalogue initially wouldn't work and Adobe support sent me off to Apple to resolve this, Apple deleted all the cache files and then it would open an empty catalogue OK and allow me to start with new photos.

However the existing and backup catalogues simply hang the program.

Catalogue has been sent to Adobe for "repair" it still wouldn't open the repaired file.

System is an iMac 27" (model identifier 17.1) 24GB memory, upgraded to SSD.
OSX 10.14.6
Lightroom Classic v8.3.1 or 8.4....