Like you I have a model with 3 AC's. While it's a known issue, Keystone will not explain to me the fix and all of my dealers are booked for months.
I FOUND A WORK AROUND! So it really has nothing to do with the outside air, but if you hold an ice pack to a sensor unit until it reads below 100 degrees, that AC unit will kick on. Rinse and repeat with all of the sensors. I was able to get all 3 units running yesterday in 114 degree heat using my generator with this method.
Called Keystone again and still got "refer to an authorized dealer"