Steps to Reproduce:

1. Factory reset iOS device ( iPhone 11 Pro Max )
2. Activate iOS device with multiple cellular plans ( Verizon SIM, AT&T eSIM )
3. Install Minecraft from App Store
4. Open Minecraft and ensure that "Use cellular data" is ticked to yes.  Sign in to xbox account.  Note response times.
5. Browse server list and attempt to connect to any server, including self-hosted.  Note performance and ability to connect.
6. Remove Minecraft, Connect to WiFi hotspot and repeat 3-5
7. Remove Minecraft.  Reset iOS network settings.  Select either of two plans under Settings / Cellular / Cellular plans and tick "Turn on this line" to the off position.
8. Repeat steps 3-5 with each cellular plan individually.

Observed Results:
Minecraft loads normally and can generate and play single player map on localhost in all scenarios.

When on cellular with multiple cellular plans activated, all in-game internet connectivity times out, or functions extremely slowly.

This behavior is agnostic of "allow cellular data switching" and is also agnostic of cellular signal strength.

This behavior is also agnostic of any graphics, audio, or profile setting or combination of settings.

Marketplace becomes unbrowsable in any manner..

Servers browser reports ping times in excess of 25k-50k ms, if at all.  Selecting any server and clicking "Play" will display "Unable to connect to world" after roughly 20 seconds.

A wireshark trace on the server side of a self-hosted server can be produced if need be.

Same installation of Minecraft works fine on any wifi connection ( even a wifi hotspot generated from another device on the same cellular account )

Same installation of Minecraft also works fine on either cellular plan, provided the other sim has "Turn on this line" flipped to the "off" position.  

Expected Results:
Normal functionality both local and network without needing to toggle "Turn on this line"  on one of your mobile numbers when running dual SIM.