EOS 5D Mark IV error with EF 28-300mm lens, other lenses OK

[orthodan]

I have had a Canon EF 28-300 f3.5-5.6 L IS USM for many years.  My Canon 7D started having problems so I bought a used low mileage Canon 5D Mk IV from a friend when he went mirrorless.  After a few shots, I get the error message about difficulty communicating with the lens - clean the contacts.  I have thoroughly cleaned the contacts with no benefit.  If I turn the camera off, then on, it works for a while then the error recurs.  Sometimes it is 3 or 4 images, sometimes 20.  I don't have the same problem with any other lens, and I don't have the problem with the 7D body.  Is this a firmware problem or a compatibility problem, or is the lens getting old.  If I am looking through the viewfinder in manual mode, I notice that there is a metering problem with the image where I get the error message.

[deebatman316]

Does the same test I told you to do on the 5D Mark IV cause the lens to act up on the 7D. I've heard of another similar issue. Lens would work fine on one camera than another it wouldn't. But trying the same test on the camera the lens was working on caused the camera to display an error code. After trying that test on the camera that was working.

[orthodan]

did the DOF thing 30 times on the 7D and took 30 photos, no problem

[deebatman316]

This sounds like Contact 1 800 OK Canon. Are the contacts on the body intact and on the lens too. No discoloration either. 

[orthodan]

One of the contacts on the lens is showing some wear (grooving) but otherwise they look OK.

[p4pictures]

This sounds like a lens fault, sometimes failing aperture assemblies exhibit this kind of "sometimes work" problem.

[orthodan]

firmware is the most recent 1.4.0

[orthodan · Accepted solution]

sent it in to Canon and they replaced the 3rd lens assembly, image stabilizer and rubber mount.  Problem solved.