Hidden Lines inside edited group

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.