Problems with exposure

[TurtleDownUnder]

I have recently bought a new Canon 5D mark IV and am having problems with exposure.  I am using an older EF 24-105 lens. I have experimented with different metering modes and still seem to have the problem.  Two photos taken back-to-back with exactly the same settings and the same field of view have dramatically different exposures.  One will be just fine, the next completely blown out.  See an example below:

ISO 320  1/400 sec f/14

ISO 320  1/400 sec f/14

Any ideas, suggestions.  Am I doing something wrong or is there a problem with the camera and/or lens?

[ebiggs1]

"Any ideas, suggestions."

Yes, your lens did not stop down.  Simple.  Are you using high speed shooting mode?

Wait, wait, did I hear somebody say "light flicker"?  

[Waddizzle]

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@ebiggs1 wrote:

"Any ideas, suggestions."

Yes, your lens did not stop down.  Simple.  Are you using high speed shooting mode?

Wait, wait, did I hear somebody say "light flicker"?  

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No, you did not.  You’re hearing voices in your head again.  

[Peter]

Then it sounds like a stuck aperture. Some 24-105/4L IS have issues with a cable, as written before.

[ebiggs1]

"...it sounds like a stuck aperture."

The aperture can't be stuck.  It might be sticking but since it works some or most of the time it can't be stuck.