The arrive/left/arrive/left/arrive/left/pattern with the Zigbee presence sensor is almost always due to local interference, typically from Wi-Fi.
At my own home, most weekday afternoons around 340 the presence sensor starts bouncing on and off the network just like your screenshot. Since the local school bus arrives at 3:30, I’m pretty sure one of my neighbors has boosted Wi-Fi and a child who gets home about that time. 
The SmartThings hub has its zigbee channel assigned at the factory and cannot be changed after that, so there’s very little that can be done if the interference is not from your own Wi-Fi network.
The first thing you can try is changing the channel that your own Wi-Fi router is on, in case it is your own system creating the interference. That can help.
Also, make sure that your SmartThings hub is at least 2 m from your Wi-Fi router at home. 3 m is even better.
Sometimes people try to solve the problem by putting the presence sensor down right next to the hub, but they have the hub right next to their Wi-Fi router, so they actually make the problem worse.
I personallyended up switching to using I beacons as presence indicators because they just ended up being more reliable for me. But this is one of those things where “all home automation is local” and a device it works great in one home may be the one that works the worst in another, just depending on the local interference issues.
If the problem is the arrive/leave/arrive/leave/pattern then you can consider the kind of approach that I use. It will not help the problems of the sensor that always says it’s away or always says it’s present, though