My 6k pro refocusing with the lens set to MF.

Hi everybody.
The camera is on a tripod, and the focus set with the AF switched on on the lens, then I switch it to MF to ensure that it stays in that focused position. The focus assist shows the confirming outline, but after a while the picture is getting out of focus.
Not sure if it is important, but I focus the camera before sunset and do the recording right after, that's when the picture is getting out of focus.
At first I thought that the lens is not good and somehow is getting out of focus even when set to MF, so, I switched to another lens but it keeps doing the same.
I thought maybe there is some kind of autofocus setting in the camera that I missed, but as far as I know there is none, right? You have to point at the object and touch the screen and it slowly gets in focus, which I didn't do.
The second camera is 6K (not Pro), and it doesn't seem to do that.
Pretty weird, huh?)
Please let me know what you think.
Thank you.

I haven't seen this behavior on my cameras at all (2 PCC4k, 1 PCC6k Pro, 1 UM46k, 1 UMPG1, 1 BMCC).
Pretty weird indeed.

Did you change the aperture after sunset?

But maybe there is a problem with electronics of the mount?

I would contact BM support if you are still in the warranty period.

Hey Robert,
thank you for your reply.
Actually, these were just the tests, so, being busy with other settings I set the iris to auto (iris only), and of course it was changing all the time because the lighting around sunset is constantly changing.
So, you think changing the iris (aperture) might have caused this out of focus shift?

It could be because when you focus to infinity and just don’t quite nail it, you won’t see it at f8 but when the lens opens up it just might go out of focus a bit. You might want to check this if it was the case here.

That might be) I'll pay attention to this next time I do it.
Thank you, Robert.