Given 
The ScreenGui and Frame are default settings. The ImageButton and the TextLabel parented to the IB cause any number of clients to crash before being able to load into the Local Server. See complimentary thread for more info:
https://devforum.roblox.com/t/cant-test-game-with-local-server-2-players/73123
Repro place:
ReproFile2 For Crash Report Local Server - 2 Players.rbxl (16.4 KB)
Note studio does not crash if one inserts the default for each of the 4 objects in that same hierarchy.