V 3 hub, smartthings buttons
I have several smartthings buttons and the two that are located in the room with the hub, a few months ago keep going offline.
I have replaced battery, that is not the issue. Each button drops offline and will not rejoin until I remove the battery. Sometimes I have to repair them to get them connected. Some only last 10 min. I have rebooted the hub. 
And advice?
Interference issues maybe? Is your SmartThings hub near your wifi router? If so, I suggest keeping those far apart from each other.
Nope wifi router is two rooms over from the smartthings hub.
I had Zigbee issues and tried many things until I sent all devices into panic mode to rebuild my mesh. Unplug your V3 hub for a minimum of 20 minutes (I did 90), leave all your Zigbee devices powered and batteries in for battery devices, then plug in the hub and let it set another 10 minutes. This can help rebuild your mesh.
Until I did this, I kept dropping random light bulbs anywhere from 10 feet to 2 stories away from my hub.
I’m curious if you resolved this issue; I just purchased a ST Button (IM6001) and I’m experiencing the same or similar issue. I have a ST Hub v2 and several other devices (door sensors, leak sensor, etc) and have had no issues with them going off line. I received the button yesterday and it connected fine and is working great, but it keeps going off line after about 5-10 minutes. If I press the button it works immediately and does exactly what I have it programmed for, and also shows as connected in the app. If I wait 5-10 minutes and look in the app again it shows as off line, but as soon as I press the button it is back online. It’s not a major issue, but definitely a quirk.