Defies logic - image not showing

Site is a few years old - Laravel 5.1

When first set up, all images (uploaded to public/images), displayed correctly using, for example:

in blade templates.

Now, I have uploaded (FTP) a replacement image called services-2.jpg and edited the blade template to change the filename - and, guess what, I get the placeholder box on the page and the image does not show. Even if I just copy the orginal image file and rename it with the changed filename - again, no show.

I have tested a new img tag on the home page - first I used an image file that was originally uploaded - that worked. Then I just changed the file to one recently added - no show.

So, just by referencing a more recent image file - it changes from show to no show. No other changes.

I have done the clear storage/framewor/cache and views folders - no change.

I am stuck as to what else might cause this behaviour - any thoughts?