Attempting to load into a world with "tweakFreeCamera": true, in the config file, or freecam set to true from the menu while not in a world, causes the game to freeze indefinitely with no crash log. When this is set to true while already loaded into a world, it is usually reset to false when exiting the world. This should prevent this issue from happening.
I ran into an instance where it was not reset to false when leaving a world, and I am unaware of how to reproduce this.
edit: I ran into this issue when loading up a new client on a new account while another client was already running with freecam on, causing it to be set to on on the new client.

versions:
malilib: 0.54.0
tweakeroo: 0.31.0
minecraft: 1.12.2
liteloader: 1.12.2-SNAPSHOT-r4CC2BB0-b4-4