People spending inordinate amounts of time memorizing solutions to common problems. This is admittedly partly the fault of HR not ensuring that interviewers have a good pool of problems to choose from and twists to put on things, but it's a constant cat and mouse game with various websites aggregating interview questions from companies.
It's pretty easy to spot when the candidate goes from canned answer to actually having to think. "Thank you, that looks good; now I need it to also do this extra thing" - keep tweaking the question until they have to think.
I’ve had reports of Zoom interview where an earpiece has fallen out and my interviewers heard advice on how to answer the question audibly present. Kind of dumb, how hard is mixing the audio?
How can a code interview fail? Hidden earpiece?