This
if ((checking_string_var = str_cmp(chat_text_line2, clean_checking)) == 1)
is always true. I think, what you want to do is
if (str_cmp(chat_text_line2, clean_checking) == 1)
This does not cause the freezing of the game, but it may help you at another place.
Freezing often happens, because you've forgotten to place a wait(1) inside a loop. There is no loop inside your posted code, but maybe, somewhere else?
