Operating system: Windows 10
Graphics card: RTX 2080
Broken: 2.80, dbfbd6b9043d, 2019-03-16 02:58
The UI (correctly) displays it switches to Object Mode if the active rig is in Pose Mode and the collection it's in is hidden. Unfortunately this locks the viewport from being able to make any new selection unless you specifically select an object in outliner. After this is done you can select objects in 3D Viewport again.