There may be two different issues, but one of them is definitely using a hue dimmer switch with a zigbee home automation coordinator like SmartThings.
As far as the other problem, we have a Gen 2 Phillips Hue Bridge and two Hue dimmer switches that we got as soon as they came out, so about a year ago, and they’ve stayed connected the entire time.
I haven’t seen any complaints in the Hue forums about dimmers with the Gen 2 bridge, but I have seen some about the Gen 1. In most cases the problem seems to be Wi-Fi interference, but I suppose it could also be zigbee interference from SmartThings.
The Dimmer Switches seem to be affected much more by WiFi and probably other noise in the 2.4GHz band than the bulbs and bridge. I had the same problem, the switches became much more reliable after changing the ZigBee channel
Fortunately, it’s very easy to change the zigbee channel for your hue bridge, you can just do it through the app, so you might try that.