Subfolder keep disappearing

I have several very important subfolders that have been active for months. All of the sudden they are gone. I can "search" emails using the folder name and will get most emails within the folder. But cannot access or see the folder.

When I create a new subfolder, it also does not show in my folders lists.

I need these subfolders!! What do I need to do to get access to the and have them show in my folders list?

Thank you