This has been happening for awhile and is becoming a real workflow problem. Both side panels (and the strip along the bottom) in Library, Develop modules will periodically and suddenly disappear and I cannot restore them without quitting LR and restarting the application. Note, this is NOT simply hitting the tab key to hide the panels. They just suddenly go away and will not come back without a restart. Any idea what's going on? It's a real problem, especially when I have to back up the catalog file periodically when I quit the program, which takes a long time.
Are the side panels BLACK, or are they not present?
If the side panels are BLACK, this was a bug that has been fixed and you need to make sure you have the latest version of Lightroom installed.