installing pocket plus is the culprit EVEN though you uninstalled it. Do a hard reset as that should bring it back to the original status. When you get stuff like this use it for a day or so without installing anything on it to see how it performs and notice the probs then when (if) you install anything you'll know if the prob was there before or after you installed the app...
I've never had that problem using calendar or the normal alarms via the clock app. That's prolly cuz i didn't install pocket plus
