Typical scenario: Editing the textures of the floor tile edging. New object each time there is a corner, so plenty of them.
Going along - select object, explode, select face, paint, texture, position, make group, and then on to the next one.
Suddenly, right-click has everything greyed out. No editing allowed. selection lines still blue, so not locked.
Exiting SketchUp and starting again works.
SU 2017 Make