I have same issue with an ic 706 I just hooked up. If you cycle the radio head power off and back on, the audio will return just like you had first turned the radio on. Every once in a while it takes 2 cycles of power. This is much faster recovery than waiting for rig to come back on it's own. So far mine only happens during transmit. It can happen anytime during the transmission, not just at the start. If I understand the lites on the remoterig, the audio stream is lost but since the yellow lite is still on, the SIP connection is still valid.
Jim
WH7CD