You probably know that your UPS can supply only 330W of load on its "battery backup" four outputs (the upper four ones). So maybe you connected Avalon on one of the four lower, "surge only protection" outputs.
He did originally, but not now:
After 30 minutes or so of mining, the lights in my room flickered, UPS's beeped and complained. Because of some stupidity (plugged into 'surge-only' side of UPS), the miner restarted as well. After some reconfiguration, this problem was solved.
since a an APC BackUPS ES-550 can only supply 330 watts (I have 2 and can can confirm that spec, its also posted online), plugging a 620 watt Avalon into the "surge only" outlet is correct - ie, use the unit only for surge suppression. if its plugged into the "battery backup" outlets the unit will likely just shut down when presented with that kind of load.
Aseras is right, get something more substantial. at the kind of coin that thing is cranking out right now its almost certainly worth it. needs 1100 VAC (650 watts) at least, so 1400 VAC (820 watt) unit is reasonable.