I now know that this was a problem when updating from 2014 to 2017. DW lost remote links then.
!) are you working in a defined local site folder?
2) is your code free of validation errors?
I have no trouble seeing remotely hosted images in Live View.
<meta name="viewport" content="width=device-width, initial-scale=1">
<meta http-equiv="X-UA-Compatible" content="IE=edge">
<h3>This is a placeholder image</h3>
<img src="https://placeimg.com/900/600/arch" alt="placeholder">
As mentioned before, this occurred specifically with the update from the 2014 to the 2017 version. Pages created and uploaded after 2017 this do not have this issue, but docs created prior that have not been opened yet in 2017 will show bad links in design mode, but display correctly in live mode. My workaround was to place local images back in place, reupload the images to the server (even thought they were already there), and then change the URLs manually to match the remote. This time, the images displayed correctly. I had to go through all my files to fix this. Remote files displayed properly in the menu.