I finally found a solution for the crashes: I reset my phone, then cleared the whole device, then flashed it... I was starting from fresh <--- this is not the solution YET I didn't install anything but wazapp nightly8. It was working fine at first. After a few hours started crashing again. Noticed it happened more while trying to access a group conversation. Not sure why, but synced contacts again. Worked better for a few uses then again crashed.. re-synced the contacts again and again. Now no more crashes at all! Apparently it doesn't sync properly in one go from the first time (got more than 500 contacts on wazapp). And when not synced well it crashes. I then installed FasterN9 and N9Qtweak etc.... No crashes whatsoever. Conclusion: Nightly8 works properly. Crashes had nothing to do with FasterN9 or any other app. Sync contacts multiple times so it syncs properly.