Yes, I have seen this issue before. After we upgraded the PPM from 8.x to 9.14.0004 we saw this issue that al other notifications were going, even notifications to SP manager and resource were going but the notification wasn't going to the RP manager. We contacted the support and they gave us a weird one-off which fixed this issue. However support also told us that download the latest patch 9.14 from support site and that would also fix this issue.
So bottom line contact support and they will help you as its a known issue with 9.14.