It's only "reproducible" if you find other 555's mixed in the shipment but not distributed to students. Depending on what the error rate in the shipment packing is, that might be very easy or it might be quite hard. At any rate, it's a stats problem that the professor is unlikely to want to engage with. Unfortunately.
For the next semester, a good prof would have a QA step or a harnass that turns on a green light if you plug in a working-as-expected package. I can see how the lab assistant job gets plenty to do in a well-run course, and also how unlikely it is to be happening in real life. There aren't enough incentives.
I suppose, although if the student is able to show the prof with the tools that the chip they have (which based on the story should be visually identical or very similar to the rest of the chips) behaves incorrectly, that test can be repeated many times. It's possible the student could have acquired it elsewhere and is snowing, but even if that's the case the fact that they can do the analysis and show (and waited so long in the class to get there), and have the history of asking for help throughout the course, all add up to pretty powerful evidence IMHO. The prof could even do his own test with the chip if he doubts. It seems hard to believe that one student would intentionally try to "cheat" by making his life much, much harder. It's surely a path of much less resistance to just follow the book.