In the meantime, it’s easy to fix as long as you remember that this is an issue and you don’t panic because you’re afraid that all your folders are missing.If the folder pane disappears, click on and check “Normal.” The Folder Panel will immediately appear.What you can do is to use Which sets the visible items to 'Folders', 'Calendar', 'People' and 'Tasks', with no other items inside the '...' (the rest are hidden as we don't use them in our environment anyway).Since 'Folders' is first in the list, it is the default for users when they open Outlook.
Update: I just found a nice way to workaround this!
No error that I could find is generated; however, the file is never saved again.
After some more poking around (it was easier to search for than for the symptom itself) it seems that the general consensus is that this file becomes corrupt more often than you would imagine.
There are Office 365 standalone plans available, but many of the limits are different.
If you are looking at a standalone plan be sure to check out this article before finalizing your Office 365 public folder decisions.