The attribute image.width has an invalid value

Is because the Images should be at least 696 pixels wide.

your image is 1

Interesting!

Is that required by the standard (and if so, why), or can I just modify the AMP plugin template to change that?

My placeholder image is 1×1 because I didn’t want to update my older articles, but for the past little while, my featured images are typically 600px wide, so they would still throw that warning.

I got the same validation issue and was able to fix it by overriding the image metadata

add_filter( 'amp_post_template_metadata', 'override_schema_metadata', 10, 2 );
function override_schema_metadata( $metadata, $post ) {
  $metadata['image']['width'] = ($metadata['image']['width'] * 1.2);
  $metadata['image']['height'] = ($metadata['image']['height'] * 1.2);
  return $metadata;
}

the multiplier would make sure that the image is in proportion, not that it matters since the display would still be dictated by the <amp-img> attributes.

I have the same image width error plus a logo error.

https://search.google.com/structured-data/testing-tool?url=https%3A%2F%2Fjobmob.co.il%2Fblog%2Fpersonal-logo-design-tips-for-non-designers%2Famp%2F#url=https%3A%2F%2Fwww.hlbenefits.com%2Fhealth-benefits-pulses-superfood-future%2Famp%2F

I still didn’t get ot how to correct this error

it’s because the image width IS incorrect. So is the height, BTW, because these is supposed to be quotes around the data part of the JSON data, {“height”:100,”width”:100} should be {“height”:”100″,”width”:”100″}. The plugin is borked.