Something about compile error

Dear developer：
Hello, I have a strange error. After I load json from a rule library, I had a error about compile failed.As follow，
“ret -4, msg = Unterminated character class starting at index 2.”
“ret” is the value the is returned, and msg is the reason of error. Specially, I think my load a right rule library, because the error will appear randomly in the same running code. For example, I will run the same program repeatedly for 10 times, and this error will occur for 3 times. The rest will work normally. So please tell me whether I did something wrong or tell me how to solve that