You have code like
<a href="89"><img src="https://www.docreit.com/wp-content/uploads/2015/09/ABTthumnail3.jpg"></a></div>
If your href doesn't start with a / and isn't a complete URL like https://example.com/, it will be used as a relative URI, and will simply be added after the current URL. Add 89 after https://www.docreit.com/about/12/ and you get https://www.docreit.com/about/12/89.
You'll have to figure out what part of your theme generates those links.