I am working on a document with a large number of pages and when I scroll through the pages I can view the first 20-odd pages, then I just get the gray pasteboard, (see screencap). hitting command 0 brings the first missing page into view, and clicking on them in the pages window will show them, but as soon as I start scrolling they disappear again. I have saved the file as an IDML, and reset Indesign preferences. Has any come across this before? I remember I had this problem a couple of years ago and never got to the bottom of it. I'm running Mojave.