High voltage input warning

I have an off grid solar system in a school bus conversion. I keep getting a high voltage warning and my solar will stop charging my batteries. I have 4, 315 watt solar panels in series coming into a 100 amp mppt solar charge controller, 6 180ah agm batteries wired in parallel and a 3000 watt pure sine inverter. I run a small refrigerator off the 110 a few outlets and everything else is 12v.
Comments
Is the voltage warning on the PV side or the Battery side ?
Have the days been unusually cool or sunny ?
i see no need to have 4 panels in series, to charge 12V battery. The voltage of 4 in series could approach the input limit of your controller, triggering a shutdown. Wired 2S2P would still allow the MPPT to function efficiently, and with less conversion loss from high DC voltage to 12V. with 2 in parallel, you would have more amps in the PV loop, but is it enough to matter - depends on the gauge of the existing wire and the distance from panels to charge controller.
|| Midnight Classic 200 | 10, Evergreen 200w in a 160VOC array ||
|| VEC1093 12V Charger | Maha C401 aa/aaa Charger | SureSine | Sunsaver MPPT 15A
solar: http://tinyurl.com/LMR-Solar
gen: http://tinyurl.com/LMR-Lister ,
Not a lot of 100 amp charge controllers out there. Could be an off brand, but I'd post a few and their spec's;
Aims; Max PV open circuit voltage: 155Vdc
https://www.amazon.com/Aims-Power-SCC100AMPPT-Charge-Controller/dp/B078VL7HGX
EPever; Max. PV open circuit voltage: 150V
https://www.amazon.com/EPEVER-Charge-Controller-Flooded-Tracer10415AN/dp/B07JVQY8QB
Renogy RVR100;
Magnum;
Here are some 315 watt solar panels with math for basic VOC voltage in a string of 4 panels (the VOC will be higher when very cold)
Canadian solar VOC=Voltage (VOC)40.1V 410.1V x 4 = 160.4V
LONGi VOC= 37.9 volts x4= 151.6 volts

These are modern 120 cell panels
Previous they would normally be 72 cell panels Like;
REC 315PE72 VOC=45.5 x 4 = 182 volts
SW315 Mono - SolarWorld VOC= 45.6 x 4 = 182.4 volts
Trina-Solar TSM-315 voc=45.6...
The voltage of strings of 4 are usually too high for standard MPPT charge controller, The Magnum can handle most of these, but the others aren't realistic.
I'd suggest switching your configuration to 2 pairs of 2 panels. You can do this on the top of your bus with "Y" connectors, Like these;
...and still use the same wires bringing the power into the bus. Check the ampacity of the wire! and your breaker/fuse size.
What panels do you have?
2.1 Kw Suntech 175 mono, Classic 200, Trace SW 4024 ( 15 years old but brand new out of sealed factory box Jan. 2015), Bogart Tri-metric, 700 ah @24 volt AGM battery bank. Plenty of Baja Sea of Cortez sunshine.