This bug is still happening. To reproduce this is what you need to do
#1 as Host
Host a Minecraft Server using Cellular Data
Invite a friend who's connected to either Wi-fi/Cellular Data
Unable to connect to world
#2 as Joiner
Ask a friend to host a Minecraft World that is open for Multiplayer
Turn off Wi-fi and Turn on Cellular Data
Join a friend from FRIENDS tab
DaddyRob
This bug is still happening. To reproduce this is what you need to do
#1 as Host
Host a Minecraft Server using Cellular Data
Invite a friend who's connected to either Wi-fi/Cellular Data
Unable to connect to world
#2 as Joiner
Ask a friend to host a Minecraft World that is open for Multiplayer
Turn off Wi-fi and Turn on Cellular Data
Join a friend from FRIENDS tab
Unable to connect to world