"Server Full" with 2/5 when trying to reconnect on iOS

Daughter playing on iPad mini 2, hosting the game.

Me playing on iPad Pro, connected to the game on the mini.

Daughter switches from Minecraft to Music App to change background music.

My Minecraft tells me that it got disconnected, OK.

A few seconds later Daughter switches back to Minecraft.

Trying to reconnect from my iPad gives "Server Full" although list only showed 2/5 connected users...