Pebble app was added to the list of non-optimized apps as soon as I was using Android 6 on my Z3c, so at least for me it doesn't solve the problem.
Just at this very moment I can go into the Pebble app, it shows me my pebble time steel (version 4.1.3) as connected but I receive no notification. I can go into the "support" menu and try to send test notifications, but neither for textmessages nor phone calls or e-mail anything happens on the watch.
I also tried an alternative software for the pebble app (open source gadgetbridge), but this shows the same problem, after some time no more notification. This means it's most likely some problem between the z3c and the watch itself. Maybe something that needs to be fixed in the firmware of the pebble or maybe it's simply the fault of the phone.
Not sure if this forum is the right way to report this to the pebble team, so far nobody showed interest in this thread...