Calls drop when attempting to merge conference call.

Hi everyone - I have the iPhone XR with Verizon. I've read into this, but can't seem to get an answer.

I do a lot of conference calls for my work. At first everything goes well. I will call the first party and it's smooth. When I add the second call the first party stays on hold and I get connected to the second party, but when I go to merge the calls to a 3-way call. The 2nd party goes to hold for a second then drops. My phone takes me back to the 1st party call, then drops after a few seconds.

Anyone else having issues like this? Should I reach out to Apple or Verizon?