Diagnosis
The most common culprit is an IP address conflict or glitch in the SmartThings app/Wi-Fi Direct handshake.
How to Fix It
On the projector, go to Settings > Connection > Screen Sharing. Turn it OFF, wait 10 seconds, and turn it back ON. On your phone, forget the Freestyle's Wi-Fi Direct network in your Wi-Fi settings, then try the connection process in the SmartThings app again from scratch.
If That Didn't Work
Ensure both devices are on the same 2.4GHz Wi-Fi network. The Freestyle 2 can have issues with 5GHz bands for screen mirroring. Temporarily switch your phone to the 2.4GHz band of your router.
Heads Up
Samsung phones with SmartThings work best. For iPhones or other Androids, use a third-party app like 'AirScreen' downloaded on the projector's app store, it's often more reliable than the built-in mirroring.