System Information
Operating system: Linux
Graphics card: GTX 1080
Blender Version
Broken: e4153946ad1
Short description of error
Tools that are laid out as Panels in the WINDOW region, PROPERTIES space (.objectmode context) seem to disappear at random moments, usually when Blender has been running for a while.
Exact steps for others to reproduce the error
No idea. But when it happens, opening the User Preferences window brings the tools back.