When Magwitch arrives, Pip is nervous. The best evidence that he recognizes Magwitch is that he lets him in. Why would you let a scruffy-looking stranger into your house? The fact that Pip does so suggests that he is aware that everything is coming crashing down on him. Consider his reaction when Magwitch asks who pays for Pip’s lifestyle.
With my heart beating like a heavy hammer of disordered action, I rose out of my chair, and stood with my hand upon the back of it, looking wildly at him. (enotes etext p. 216)
If he does not suspect that this is his convict, and he is the secret benefactor, why would he react so strongly? You would expect him to fear being robbed, not fear what Magwitch would say.
When he finds out why Magwtich is there, and Magwitch begins talking about how he made Pip a gentleman, Pip is crushed but not actually very surprised.