Running a MackBook Pro with 16Gb Ram, and I made the following changes:
1 file changed, 2527 insertions(+), 8451 deletions(-) and then tried to commit at which point SourceTree locked up, and each time I try to restart it opens in the same place and gets stuck, and eventually crashes. I have noticed over the several months that SourceTree has been painfully slow, and at times nearly unusable - they have some serious scaling issues with large files and large repositories.
Maybe this will help - the log from my crash:
Process: Sourcetree 
Version: 3.0 (200)
Code Type: X86-64 (Native)
Parent Process: ??? 
Responsible: Sourcetree 
User ID: 501
Date/Time: 2018-11-06 11:57:37.882 -0800
OS Version: Mac OS X 10.13.6 (17G65)
Report Version: 12
Anonymous UUID: 6A062F06-6AB3-256F-1F4C-A33A818D2B55
Sleep/Wake UUID: 8F31785B-5E95-4052-ACF2-F6914838CAC4
Time Awake Since Boot: 970000 seconds
Time Since Wake: 16000 seconds
EDIT: I cut out the rest of the log since it no longer seemed to serve any purpose, when I filed the ticket as suggested below, where I posted the entire log.
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