Perfomance degrades for zero reason

[getho]

I load my project. I hit play on my timeline. Video plays.  I go off and do something else, come back to premiere and it wont play.  THe halftone effect on one of the clips seems to be the culprit.  Edit: this time around it was a text object in a nest. Even looking at the nest sequence it would not display it. No other effects, 1080p sequence.  The layer below contains a png. Is this a PNG issue? 

Why would it work on first play, and then not again? And why is this effect causing ppro 25 to fail, when the whole timeline plays absolutely smoothly in ppro 24.  

[Ann Bens]

When my timeline refuses to play, I minimize the program, resize and then usually the timeline plays again.