There is no remedy for mute call but for VoLTE I find if we improve UL KPI like PUSCH, SINR, UE PHR, UL BLER there will be big relief.
For this we need to reduce overlapping.
Yes low sinr as well leading to dl RTP bytes 0.
Note: There is one very good tool developed by Alcatel Lucent guys named eDAT, I find that tool very useful during VoLTE analysis.