I've seen this happen in my campaigns a few times. I've had some regions that have very low public order (makran, the one next to it and the other Seleucid region close to Armenia) that have very low public order but won't rebel. The public order was at -99 for many turns (and around -10 predicted difference? public order in the brackets) and even though on the message board it says that there are rebellions in those areas, I can't see them and public order does not increase, which messes up tax and province income.
Just wanted to let the developers know.
Great mod btw!