Hi @Dan C,
I don't know if they are related, here the screenshot too.
I Must say that the lines are random and disappear after 5 or 6 export and I can use the export without any issues until I restart affinity.
for the Bulk it may be related to a cache issues or a time to process limit as he try to perform a consuming process with 16 photo at the same time.
For the export, in my mind this is related to the software, I'm not even sure that you use GPU Hardware to make the export to Jpg.
I've tried several time the unchecking doesn't solve any of the two issues.
EDIT : To be complete, there is no crash report with the Force Exit.