About the DFS:- Dynamic Frequency Selection is the feature enabled on radios.Which helps them when they come into the contact of radar.But that's the theoritical fact. The real fact is how DFS works. When ever the radio sees any external energy on current channel it will consider that as radar.Hence you get the DFS detected message. Your findings were correct during the lab test.
Now this can be due to the SM at one perticular section is transmitting at high power.You can find that SM by taking down time from end customer and turning off each SM one by one or disconnecting from AP one at a time.And try to find which SM during the shut off time doesn't cause DFS to AP.That's one way to find.
Yes,enabling Automatic Transmitt Power Control can help you in this case.
An AP can control registered SMs’ transmit power level such that a desired receive target power is
seen at the AP. This feature is useful in DFS regions so that signals from close-in SMs are not
being received at excessively high power levels which may cause the AP to false detect. It is also
useful for managing the general RF environment and controlling effective sector size by ensuring
that SMs don’t transmit at any higher power than required.
I hope this will help rectifying this disaster and false issue.