Obi200 and outgoing calls continue with ring tone in background

[DaveOverton]

I have a few people I help out with their voip lines, 2 of them are using specifically OBI200's just recently acquired.

On occasion (once a day or more) when they make an outgoing call, things progress normally, until the other party answers the call.  Then the ring sound continues, and even the called party can hear it.  It never stops even after quite a while, but hanging up the call and making it again seems to fix the problem for that call.
Any thoughts?  Any hints?

[drgeoff]

Same or different ITSPs?

[DaveOverton]

Calling from a line using  voip.ms to ATT usually, but sometimes not.