Logic Pro X session players blank at certain points on timeline

Recently I have noticed that the session players (keyboard, bass, guitar) will be blank in certain sections even though I have added them directly.

Screenshot shows an example, there is nothing generated from measures 1-17 on the timeline, then it kicks in at measure 17.

Yesterday I was working on a piece and there was a piece missing from the middle of a session player's region, but if I moved the region the 'gap' would stay static in relation to the timeline.

Today's incident happened with a new document based on a regularly used template. I have not experienced this before, although I have previously found that the generation of session player tracks can slow down if there are many instances added.

I really don't know where to start investigating this. I have the latest version of the software (11.0.1).