Some uses have experienced issues with the iOS versions of Strike! Ten Pin Bowling and Bulls i – namely their Game Center data seems to be missing or they fail to find opponents in Multiplayer games.
To fix this, simply log out of GameCenter and back in.
Here is a video demonstrating how to log out. Be sure to check for your version of iOS as the process can vary depending on the version. To log back in – just launch Strike! and follow the on screen Game Center prompt for logging in.