I really appreciate the suggestions cdc.
Using a Sony A7R iii.
Deleted (User>Library>Preferences) com.phaseone.captureone11.plist, deleted entire user library cache (User>Library>Caches).
Reset PRAM. I was using a previous version when this started. I updated to the latest and it did not resolve the issue.
Tried exporting another 219 files from the shoot yesterday and the same errors with various files which stalls the export.
I get a spinning pinwheel of death and I have to force quit C1 to get the process queue working again btw.
C1 is my workhorse. I'm baffled by this issue. I've wasted a huge amount of time on this, hours and hours. Time I planned to spend organising the files from the daily shoot

Again, I would really appreciate any suggestions!!!
This is part of the crash report I get every time FWIW.
Process: Capture One 11 [317]
Path: /Applications/Capture One 11.app/Contents/MacOS/Capture One 11
Identifier: com.phaseone.captureone11
Version: 11.2.1.38 (11.2.1.38)
Code Type: X86-64 (Native)
Parent Process: ??? [1]
Responsible: Capture One 11 [317]
User ID: 501
Architecture: i386
Date/Time: 2018-09-06 09:53:44.713 +0300
OS Version: Mac OS X 10.13.6 (17G65)
Report Version: 12
Anonymous UUID: 05F1DCC8-BEC5-9668-CB7C-03DCEBCA8A4A
Time Awake Since Boot: 2700 seconds
System Integrity Protection: enabled
Crashed Thread: 0 UI Dispatch queue: com.apple.main-thread
Exception Type: EXC_CRASH (SIGABRT)
Exception Codes: 0x0000000000000000, 0x0000000000000000
Exception Note: EXC_CORPSE_NOTIFY
Application Specific Information:
Caught a SIGTERM. Calling abort() to get a crash report from the system.
Performing @selector(resumeProcessing:) from sender POSkinButton 0x60400019d260
abort() called