By 'automatic', do you mean that infinity:
1- Is subconscious
or
2- Can blocks attacks that Gojo can't detect
?
Based on Gojo's explanation, it is 1, so attacks too fast for his perception should bypass Infinity. His senses needs to recognize a threat first (based on mass, speed, shape, Cursed Energy, etc.), and younger Gojo said that he is having trouble identifying poisons. The process of identifying threats also puts stress on Gojo's brain, so he needs to constantly heal his brain to keep Infinity sustainable.
Of course this is not a weakness within JJK since Gojo is believed to be the fastest modern Sorcerer, and his Six Eyes (which is stated to be required to make full use of Limitless) improves his senses and perception.
But a theoretical much faster character, like one from an other verse, should bypass Infinity if he is too fast for Gojo's perception.