One issue we came across was that the client had their site is a folder called /WordPress
We moved the site into the main domain, however, lots of links within posts and pages were still referencing the old URL structure.
This means that it was looking for images in the url
To fix this we installed and run the plugin velvet blues update urls
Now, this plugin hasn’t been updated or supported for over a year so we made sure we took a full website backup prior to installing it.
Once the plugin had done its work (in a few seconds it fixed over 2500 urls) we then uninstalled the plugin to help keep the website safe.
So if you need to update some url's this could be a quick and simple little fix