Hi,
There could be multiple reason , please find some common cause behind call muting in VOLTE.
1.) Please check mute calls come from any specific handset model.
2.) Poor 4G RF condition may increase packet loss and High BLER/High Jitter.
3.) Please check if there is any frequent Ping-Pong Handover happen.
4.) Check PDCP data decoding parameters/RLC PDU sequence number length its different value in same clusters sites can cause muting problem.
5.) Check Featue status i.e. ROHC,TTI bundling enable or not .
6.) Check PCI/PRACH planning .
Thanks
Regards
Manish Vyas