A POSSIBLE FIX!
Getting help from Crandon services (here in Australia) has helped me a great deal.
I had to rename all my PDF’s first. A crash may occur if the PDF file name is very long. Do this using the references menu, file attachments, rename PDF’s - you can select multiple references at once.
I then had to also search for any large PDF files in my End note library folder as a crash may occur with files that are too large. Any larger than 5MB I have now removed from the library into a folder on my hard drive.
In the testing phase now, but it seems greatly improved from before.
Consultant suggested making note of any reference that crashes, and taking out the PDF’s attached to move them into a folder on the hard drive for easy access if needed.