Focus ring slippage?
My tamron 70-300 exhibits a similar behavior to the canon 70-200 f4 (i think) Where the focus ring will occasionally slip when focusing closer away from infinity, with the lens in a vertical position pointing up shooting the ceiling/sky above your head. Auto focus works like a charm.
It doesn't really affect my shooting but I just want to know if it's "normal" (i.e. a known you-have-to-live-with-it issue with this lens) or if it's something I should look at before it becomes worse.
I bought it used and it didn't show up during testing. I'm not sure if it's under warranty but even if it is I am not sure warranties are honored to second-hand users.