Just one menu icon won't show up

I have menu_icons working fine in all respects across my site and menus in various window width layouts/sizes, but just one of my menu item's menu icons won't show up. If I change it to another image it still doesn't work. When I attempt to set it to the image I want that is uploaded to my public files area, all I get is that the menu item text is shifted as if the image icon should be there (left padding shifted) but the image isn't created and thus isn't shown.

When going to the css background image source address pulled from rendered page code, I get an ACCESS DENIED page rendered by the Drupal site. Other menu item icon images show up fine this way too, just any image set on this one menu item that is for a panel page that doesn't show up. Is there anything anyone can think of to help point me in the right direction on fixing this without rebuilding an entire panel page all over again?

I've flushed cache twice.
I've ran cron.
I've taken the site out of maintenance mode and flush cache twice as well as run cron again.
Cleared cache on the Performance page.
I've tried changing the image source multiple times to different image files that are working for other menu items as well as other copies I've tried of the image I want to use.
The base image is in the correct location and that same location works fine for other menu items' menu icons.
The image styles folders for the rendered images are in place but the image in question is NOT there for one of my resp_img image styles settings folder.
I've flushed all image styles via the Image Styles settings page.
I've individually flushed the one image style that's not rendering this one particular image.
I've turned off an icon for that menu item, saved and then reset the icon to be on and set the correct image source url. Tried this several times.

Nothing is clearing this one image's image that was never created and thus allowing it to recreate it, thus it's not showing up for my "standard" responsive breakpoint size layout. Other breakpoints /image style show fine and the images are in those image style folders.

How can I flush this? Maybe I'll just upload that one image already resized in the location and file name it needs. Maybe I'll have to rebuild the whole page or the menu item pointing to it.

I just thought this was interesting and figured it would be good to document how this scenario would play out to fix a stray image without creating the image "by hand" and placing where it's needed as this may or may not be a continued problem in the future with other menu items (but isn't now and thinking it won't happen again, just some code got messed up for this one menu item). Thanks for your time.