I haven't seen that but nowadays I am resetting network settings and rebooting the phone to see if that fixes the issue. Hopefully that helps. That issue would drive me bonkers.
I get it almost daily. Seems to happen if I have my phone open (unlocked). There is nothing you can do to answer the call, even though it says you have answered both. I have tried merging, swapping, ending one of them. Nothing you can do.