Hi, thanks for the quick reply!
I was using Easy Installer 6.5.0 build 4 since that was the latest version from official Toradex servers, and it seemed to make sense to use that one since I am using Torizon OS 6.5.0.
However, I have just tried again using Easy Installer version 5.7.5 build 19, which is also available in the image list on the Toradex, and that works correctly, installing the image and then automatically rebooting and running the program. I have gone back and checked with version 6.5.0 again and that one still gets stuck on 100%, even though the image has been written successfully.
I have tried each version twice just now - the same behaviour happened each time, with 5.7.5 successfully installing and rebooting, and 6.5.0 getting stuck on 100%.
I will continue on with 5.7.5 then for now, thanks very much for your input.
tl;dr: Solution is to use Easy Installer ver. 5.7.5