The DL/UL_DTX_AMR_FR/HR are recomended when the EN-TFO and EN-AMR-NB are enabled, but we faced this problems within area with DTX and in other without DTX . Also we have problem with EFR but the SQI is less degradated and there is no complains.
The sqi decreased in the same time for both mobile.
I think that there are some problems with TC or MSCS, or GW because the tfo parameters are the same but the problems are located in one mscs and gateway.
What is your sw version, B10 or B11 and is the TFO activated in your system?