I just received my set today and I have this fog-like effect on the lens:

At first I thought this was due to the soft transparent protector sheet covering the lens. But even after I removed it I could still see this fog! So I went back to my 2016 set and removed the protectors and OMG...

I don't know if this has been discussed before on this forum or elsewhere... but I can't be the only one seeing this! I'm not a chemist but maybe the soft plastic covering the lens has some compound that degrades, like under higher temperatures (it's over 108F today in Arizona).
I never saw this effect in pre-2016 sets. Here is an image of my 2016 dollar seen through the lens (pretty lame):

Thank goodness, the fog is not on the coins. So... I tried to clean the lens with a soft tissue & soap / water - NG. The only thing that helps is to gently rub Olive Oil (Extra Virgin mind you) on the lens:

The lens do become greasy but at least I have a better view and can finally appreciate my coins without cracking the lens open.
Too late to return my 2016 set. For now I am happy with the EVOO restoration - which hopefully does not turn into a vinaigrette over time.
This is the above after EVOO restoration:

But on the 2017, there is far more serious problem... see the next topic...