I figured out how to join games since the new iOS update, but when I find my friend and click join game, this is the message I get:
"If you're seeing this message, something may have gone wrong while starting your game. Please post in the Technical Issues or ROBLOX Mobile forum with details on how you got here. Sorry about this."
I have deleted and redownloaded the app. iPad air 2, most recent version of iOS
For others who had a hard time finding out how to join game, go to groups, click online. Click specific friend and click show profile for them. Then you can invite to party, join game, etc (if join game works for you)