Might be too late to mention, but this is still happening in the current version (2.11.2). Since I was just writing my own post, I saw this in the suggestion window and figure I would put my findings here.
Usually the right page will remain black until one of these happen:
- go to another page and back
- go out and back into Panels app
- close and reopen the comic
Happens when switching via swipe since tapping to change pages seems inconsistent now (not sure why, could be another issue on its own). I have only noticed it happen on the right side while going through the comic. Has happened on many, but not all, comics. It happens with page animations on and off and is more likely when going through pages faster. All files are .cbz (store method without compression) of varying sizes.