I was watching Episode 5 recently and something strange come to my eye. When Luke arrives at Dagobah it seems that neither Yoda and R2D2 seems to remember each other.
As far as I know R2D2 never had a memory wipe according to Star Wars wikis and this question: Why was C-3PO's memory wiped, but not R2-D2's?
I don't know if R2D2 knew Yoda personally but he should have known him. For Yoda it maybe was just another R2 unit.
Is there a universe (Legends or extended) explanation why R2D2 seem to doesn't know him?