You should start debugging with your server logs i.e. check if they contain any clues as to what happened when the crawler was requesting a given resource.
A sample log line would look like this:
834:2a03:2880:ff:16::face:b00c - - [12/Jan/2019:18:17:31 +0100] "GET /wp-content/uploads/2018/11/alpha.jpg HTTP/1.0" 200 534066 "-" "facebookexternalhit/1.1 (+http://www.facebook.com/externalhit_uatext.php)"
Note that the response code in this example is 200 so everything should be fine.
Without server log access we can try to emulate Facebook's bot and see if everything is OK.
Checking your URL with
curl -I 'https://signs.adventistchurch.com/wp-content/uploads/sites/26/2019/02/Pg44-GettyImages-867175514.jpg' -H 'pragma: no-cache' -H 'cache-control: no-cache' -H 'upgrade-insecure-requests: 1' -H 'user-agent: facebookexternalhit/1.1 (+http://www.facebook.com/externalhit_uatext.php)' -H 'dnt: 1' -H 'accept: text/html,application/xhtml+xml,application/xml;q=0.9,image/webp,image/apng,*/*;q=0.8' -H 'accept-encoding: gzip, deflate' --compressed gives the following answer:
date: Tue, 05 Mar 2019 08:31:32 GMT
last-modified: Thu, 28 Feb 2019 03:06:49 GMT
cache-control: public, max-age=2592000
So either everything should be fine or we're not treated as Facebook's bot.
I can see that you are using WPEngine as your hosting provider, which might do some wonky checks/redirections even if the examples they give shouldn't apply.
They do admit that it could interfere with Facebook's bot, though:
WHEN SHOULD IT BE TURNED OFF?
If a service you’re using to scan your site is having issues or receiving a 301 redirect, there’s a chance this is due to the redirect bots setting. For example, using Facebook’s URL debugger tool attempts to scrape a specific page of the site that ends in a number, using one of the well known user agents that is redirected by default. This causes the tool to show an error. With this setting turned off, it allows Facebook to properly scrape and analyze the data given.
So it seems like you should try turning it off and checking again.