When loading a world with a function containing a file name containing an invalid character, the game freezes and produces the following error in the output log
MinecraftServer Encountered an unexpected exception, g: Non [a-z0-9/._-] character in path of location
custom/foo [error here]/bar.mcfunction
This causes the game to freeze as `[` is an invalid character.
[17w49b] Client thread/FATAL: Non [a-z0-9/._-] character in path of location
Game crashes when a colon is entered after a slash or another colon in commands