Yeah I just had this happen to me tonight. I created the room. My friend was able to pop out and then in again to collect the bonus hearts for the summon. He was able to continue summoning. After I used up all of my summoning materials, I then tried to pop out of the room to collect my rewards to continue summoning. Now he is still in the room on his machine but I do not see it when I join the friend summon.

Very Disappointed about this.

Okay so I just tried to restart the game to see if that helped and it allowed me to create a new room that was still at the lvl 10 from earlier. My friend however had to back out of our previous room and join the new one.

Also, I had collected 3 hearts from the quests and we had to create a new room for each heart as the resource indicator thought that I was using them all up on each summon. So three rooms later I was able to perform all of the summons at level 10 (assuming that the level indicator of the room was not as bugged as the heart resource indicator).

Thank you for the reports, we'll look into that. The room level itself is correct it will stay at the last level you participated in a friend summon until you stop doing friend summons for over an hour.

We pushed out a mini update this morning. The problem with the Heart count resetting between 2 friend summon should now be fixed.
Sorry for the disagreement.