Thank you for your post!
This behavior occurs due to adding a script to the field. It causes a Grouping, which is why your Work Around works to repopulate the Hide Object When calculation. The group of objects itself doesn't include a Hide Object When calculation until it is added after grouping. However, the previous Hide Object When still exists on the field and should still work.
I hope this helps, but if I have misunderstood something just let me know!
That is correct, but it took me a long time to understand what and why this happened.
Perhaps in a future update, you could look at least notifying the user that their hide object when condition is applied but it is an item that is part of a group, rather than just leave the field in the Inspector bar blank, which I think is misleading.