What does "Failed parsing 'srcset' attribute value since its 'w' descriptor is invalid." mean?

Question

I get Chrome errors on my website that say:

Failed parsing 'srcset' attribute value since its 'w' descriptor is invalid.
Dropped srcset candidate http://i2.wp.com/domain.net/wp-content/.../image.jpg?resize=425%2C200

Any idea what this means?

I am using WordPress as my website platform. I also use its Photon feature (within its Jetpack framework). My suspicion is that it has to do with this feature. Are image dimensions getting specified incorrectly or something?

What are 'w' descriptors?

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UPDATE: Here is the HTML:

<img src="http://i1.wp.com/gaithersburgpsychologist.net/wp-content/uploads/2015/02/lightbulb.jpg?resize=425%2C200"    srcset="http://i1.wp.com/gaithersburgpsychologist.net/wp-content/uploads/2015/02/lightbulb.jpg?resize=425%2C200 w, http://i1.wp.com/gaithersburgpsychologist.net/wp-content/uploads/2015/02/lightbulb.jpg?resize=450%2C320 w"    sizes="(min-width: 768px) 720px, (min-width: 992px) 700px, (min-width: 1200px) 850px, calc(100vw-20px)"    alt="Change your thoughts and you change your world."> 

Answer 1

I had a similar error:

failed parsing srcset attribute value since it has an unknown descriptor

and the problem was caused by a space in the image path URL.