Like the poster at https://www.obitalk.com/forum/index.php?topic=2824.0 and others, I have received notification from the people that I have been speaking to that my voice goes in and out. I had the problem a lot last year and now, in the past week or so it has begun again. Using Obihai 110 with Google Voice.
Same symptom?
I suggest that you turn off each computer or disconnect the Ethernet for testing. See if choppiness remains. If not, turn on/reconnect each computer and test for choppiness. If it does, suspect that something on that computer is consuming excess bandwidth (probably upstream). If you don't see the choppiness, start applications that you had running previously. Servers, such as torrent applications, and viruses that you do not yet know about are possibilities.
Have you made changes in your modem, such as setting up QOS or special SIP settings? Try reversing those changes.
Pinging, particularly over a long period, can be useful. Pinging your OBi, Pinging your SIP server if you know that, and pinging something independent, such as 8.8.4.4, continually can be useful. Check the recent pings whenever you experience choppiness to see if you see a correlation.