Question Lens is losing focus randomly

[Filmmak3r]

I recently bought a used Rokinon 35mm T1.5 AS UMC lens. So far it's seemed to function without issue, however, I noticed that it has been losing focus after being tilted up or down. I noticed it while trying to film a close up shot of a doorknob. I had knob in focus and I had made sure of this a couple times. After tilting the camera up and then back down to reveal the doorknob the shot was out of focus. I tried focusing again thinking maybe I had nudged the focus ring. I repeated the shot again with the same result, my shot was out of focus again. This is kind of concerning and I'd like to see if anyone else has had this issue or know what the issue might be.

Thanks!

 

[Ralston18]

Camera link:

https://www.amazon.com/Rokinon-DS50M-NEX-Frame-Mount-Cameras/dp/B00N5TM28G

Camera specs from link:

• New DS line that is color matched with other Rokinon DS lenses and have unified gear and aperture positions among all Rokinon Cine DS lenses
• 46.2 degrees angle of view on full frame cameras & 30.8 degrees angle of view on APS-C
• Features de-clicked apertures and follow focus compatibility and includes removable lens hood, lens pouch, lens caps, instruction manual and 1 year Rokinon warranty
• Minimum focusing distance of 1.45 ft.; Uses filter size of 77mm

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Not up on my camera terminology (aka marketing speak); e.g. "follow focus compatibility" per se. Check the user manual to ensure that some other setting has not been changed that could impact focus.

If the camera/lens was working and can be proven as no longer working then there may be some warranty available for repair or replacement.