Very tricky issue to track down, but basically:

  1. wifi calling works for making and receiving calls
  2. certain group SMS and MMS will not send when wifi calling is enabled
  3. a simple SMS to a single recipient will work most of the time
  4. disabling wifi calling will allow the pending messages to be sent
  5. I do not see any network traffic associated with the attempted sends that don't work - it's like the phone has decided not to use the wifi to try to send it, but doesn't fall back to radio either.... so it's just stuck. I know this because
  6. SMS/MMS over radio works fine

"Tricky" is right. I experience this too, sometimes it fights through, other times I have to play with my WiFi connection in order to get MMS to send.
Who's your carrier? According to Mint Mobile, this is expected and nothing can be done.

To mention a point I failed to mention above, the behavior seems to be specific to my home network

  • de0u replied to this.

    pixeldust99 To mention a point I failed to mention above, the behavior seems to be specific to my home network

    Interesting! Does your home network support IPv6?

      6 days later

      my ISP doesn't support, so I have IPV6 disabled.

      9 months later

      Any updates on this? I have a Pixel 7 with the exact same issue. Calls and individual texts with just text work great. But group texts and individual texts with GIFs or texts sent as MMS are stuck at sending. Also not receiving group texts either.
      Does this only affect Pixel 7 users?

        ToughDBlue Does this only affect Pixel 7 users?

        I have P8pro and it works fine there, so possibly? Or maybe it is carrier specific? As in some issues with a carrier APN settings?

          @ToughDBlue 's experience sounds exactly like mine. I have no resolution to this and have just been periodically disconnecting from wifi when I'm at home to see what SMS/MMS messages will come through. Half the time, as soon as I get off my home wifi network, I'll get a flood of SMS/MMS.

          I would really love to dig into this more deeply but I lack the knowledge of Android to debug it.