Because the issue appears only with that specific lens, on multiple camera bodies, and in both RAW and JPEG, the most likely cause is contamination or damage inside the lens rather than a camera sensor or file-processing problem.

A fixed bright patch in the same part of the frame can be caused by dust, debris, haze, or some other material stuck on or inside a lens element. Stopping down can make this kind of artifact more defined, which fits your description. One community report described a very similar issue caused by something attached to the inside of the glass, and a service resolved it.

Check the lens carefully for dust or marks on the front and rear elements, but if nothing is visible externally, the problem may be internal and require professional cleaning or repair.