12/1200 inverter occasionally stumbles and resets

I have my 12/1200 wired in with 4awg to 4x li-time 280Ah bats in parallel. the inverter’s only job is to run a window ac. Which, when running full load pulls about 850 wats at the hot part of the day, and more like 600 in the early morning hours… Occasionally ( 1-2 times a week), when the compressor trys to come on the inverter will give out this long buzz and then it will shutdown and reset… 99% of the time when the compressor comes on the inverter will give out a short buzz, (about 1 second) and then all is good… but when it “stumbles” the buz is more like 3 seconds… When it does fail, i get a low battery voltage and an inverter overload in my remote console. but here’s the thing, the batteries are at over 90% and are showing 13.18v on the VRM. the low voltage warning shows 12.99v, and I’ve gone in and checked the settings in the inverter, low voltage cutoff is set at 11v, and reconnect is set at 12.4… the overload alarm shows 0.0A… so i’m a bit stumped… the other part of the equation is, this only happens in the morning or evening when it’s cooler, not the heat of the day when head pressures would be higher in the AC… so, i don’t get it… any thoughts?