Have you tried removing g722 as a allowed codex. I normally have to do this on the Panasonic phone system as we had customers complain about the sound on the NT 5xx phones on the NS and found the they didn’t like the high def audio and used to say it was muffled and poor quality

Made g711 first preference and they said it was much clearer. I think it was coming from TDM they just didn’t like the tone of high def

“I have not failed. I've just found 10,000 ways that won't work.”