After applying masks to an image, all masks fall off and require update to appear again, and if not updated on each individual photo, they do not apply upon export. After updating an image, moving on, and then going back to that image all in the same sitting, the masks still fal off.
AI masks are stored in 'catalogname.lrcat-data'. Sometimes this package becomes 'Read only' for some unknown reason. Check this and change it to 'Read & Write', otherwise Lightroom cannot store the masks and so they will need to be updated again and again.
p.s. i don't think the adobe website, and forums in particular, are easy to navigate, so don't spend a lot of time searching that forum list. do your best and we'll move the post (like this one has already been moved) if it helps you get responses.