I have two ring groups. First group only has receptionist (100). This phone can answer calls without issue. If that call goes unanswered, it overflows to a group with each other extension in it as well as a ring all strategy. However, although calls are ringing the overflow group members, when they attempt to answer the call, all they receive is dial tone. These are yealink 42S phones. Firmware is the same on all phones. Please help if you can.