When using widgets to display images, images sometimes disappear, though image selections remain in edit view mode

[caaster]

This is a user reported bug that has happened a few times. I have never been able to repeat it, hence my delay in reporting. I am recounting the most recent instance in this ticket. Exhibit builder reported "all my images have disappeared from the home page" (https://exhibits.stanford.edu/california-as-an-island). Here is a screen shot of what he reported:

When I navigated to the dashboard to view the home page in edit mode, this is what I saw:

As of this moment the exhibit builder has not remediated the problem. However, the fix is a manual & easy one, albeit annoying. He simply needs to re-add all of the same images in the same widget (deleting the "bad" ones that currently appear in edit mode without a thumbnail), and the images will once again display.

In case this is of any assistance -- in looking at this user-reported bug, @blalbrit noted:
"It looks like all of the images in that widget are being called by URLs that are not correctly formed. For instance:
Request URL:
https://exhibits.stanford.edu/images/undefined/full/!400,400/0/default.jpg"

[caaster]

YAY!!! I was able to cause this error to occur just now. I was editing a published exhibit, Secret Service. I was trying to add an additional item row widget to the bottom of the main about page. When I did that, it caused the images in the existing item row widget above (on the About page) to display the word"default" where each image is supposed to be. However, in the dashboard view, the names of the images along with their druids still show in the item row widget. Please see Secret Service exhibit now (sorry I removed the second item row widget I just added), but everything else is left in the state I described above. For any logged behavior, this happened about 3:10 pm on Friday, 8 Dec 2017. Unfortunately I am unable to repeat it.