How is it that, per Jedi Grrrl
As for Obi-Wan, he forgot all about R2-D2 and C-3PO after spending three whole movies with them
I know people might say "well, would you remember a toaster you had 20 years ago" but really these robots have a personality, and C-3PO is probably fairly unique having been hand-built by Anakin. How many people do remember cars, computers, TVs, and so on they used and interacted with throughout their life, or even closer, pets and work animals? I'd say most.
So, other than OB-1 being a clone, what possible in-universe reason could be given for him totally not showing any sign of remembering these droids?
(It's a teensy bit easier to believe that Darth Vader doesn't show recognition of them given him being possessed by the dark side and being so busy terrorizing the galaxy and all)