If it is only affecting PSTN calls, then I would disable all of the following:
DetectCPC
DetectPolarityReversal
DetectFarEndLongSilence
DetectDisconnectTone
If both caller and callee hang up after the call, then the call should still disconnect.
If the above solves the problem, then enable each parameter that you think you may need. Personally, I would never enable DetectPolarityReversal or DetectFarEndLongSilence, but this does depend on what country you live in and local PSTN line signals.