CO 21 (Express) crashes my computer when I try to export a file

I use Mac OS 10.13.6. (1.6 GHz Intel Core i5) and downloaded Capture One 21 (Express version), build 14.0.1.7. It worked just fine for the first 25 images, and after that it crashes my computer when I attempt to export a file (every single time).
I tried this (https://support.captureone.com/hc/en-us/community/posts/360014357858-Capture-One-21-keeps-crashing-on-load) several times but it didn't help.

I'd be grateful for any ideas, though my level of technical expertise is such that you'll need to explain it to me like I'm a four year old child.