iMessage ignoring “Start new conversations from” setting

[verdi1987]

Line 1 is 11 Pro is running iOS 13.7
Line 2 is XS Max is running iOS 14 beta 8

Both phones numbers are enabled on both phones under Settings > Messages > Send & Receive.

Both phones are set to Line 1 under “Start new conversations from.”

No matter what I do, new iMessage conversations from Line 2 always use its number as the Caller ID instead of Line 1’s number.

I have:

• Deleted existing conversations prior to composing a new message.
• Verified that message is sent as iMessage.
• Deactivated and reactivated iMessage.
• Toggled the outgoing number to Line 2’s number and back to Line 1.

This may have been broken for a while, so I am not certain if it’s due to iOS 14. I always trusted that setting worked, so I never verified that it does.

Is anyone else experiencing this?