Use of the Hide command to control visibility while modeling often leads to confusion.
Best to use it sparingly and only in the topmost modeling context. Here’s why.
Edit > Unhide > All … Works only upon entities hidden within the current modeling context.
Edit > Unhide > Last … Works globally just once.
After that, the Unhide command is context sensitive.
Consequently, un-hiding entities hidden within groups requires re-enter their editing context to Unhide.
The aforementioned handy little plugin will unhide all your hidden entities in one go.