On the display of the affected WTR-680 beltpack the transmit frequencies read the incorrect frequency, that is it reads 704.225 instead of 704.200 for group 02a.  Same for any of the group 02a transmit frequencies.  I suspect the the RF tuning on this beltpack is off which might be causing the issues the customer described.  Since this isn’t a user adjustable setting the pack would probably need to be retuned by factory trained service personnel. 
Customer is going to see if a user programmable group will temporarily work,  a user programmable group on a WTR beltpack are the groups from 25 to 36, customer can program in their own custom frequencies that fall into the RF band of frequencies for that system in 25kHz increments. 
For example on a C6 band system the two 18 MHz wide frequency ranges are:
C = 554 MHz to 572 MHz6 = 704 MHz to 722 MHz
The user can only program fcustom frequencies  within these ranges on a C6 beltpack.