Inbound route definition for Zap channels intermittant

I have been trying to define inbound routes with my TDM400P. I have been attempting to send the 1st 3 channels to IVR A and the 4th channel to IVR B. I have defined the channels in the zapata.conf file however, this seems to be intermittant. Most of the time, the calls proceed as directed, however, on several occassions (and in each occassion I have not found any indications on any log files) the 4th channel will go to IVR B or more often, channels 1-3 will go to IVR B.

Am attaching a copy of my zapata.conf file, extensions.conf file, and extensions_custom.conf.