We are running into the same symptoms. Did you find an answer yet?
Are you running GlobalProtect VPN client when this occurs?
Are you running the Citrix Client when this occurs?

We have been reporting this issue for years. We have Global Protect but had the issue before, We seen this issue allot after RC pushed an update to RC Phone to removing 20.4.0. RingCentral told us to go to MVP.. Still have issue.

On the RC MVP we got into Development (CTRL + Shift + D). Once we are their we selected Open WebRTC tool, then select create dump, selected Enable diag audio recording. This open a place where you can dump the audio and dump. We do this at the start of each call until the issue occurred. Then we compare the audio of the dump (local to the agent) to the CXOne audio. The Dump Audio is clear where as the CXOne audio has the issue.

Now we are being told that Level 3 is saying installing MVP by running the exe file can caused almost the same issue. We are now trying to install the MVP msi file to correct this.

What we notice two items.

1. If you look at the CXOne audio file the agent voice is distorted where the customer can't understand the agent. After 10 to 20 seconds the audio is clear no issue.

2. If you look at the wave file in CXOne you will notice that the agent wave length is amplified after 10 to 20 seconds. Allowing the customer to hear better.