After updating phplist from 3.2.4 to 3.2.5, with the plugin at version 2.0a4 in both the phplist installations, one image file linked as URL doesn't pass the image file test and I'm unable to send message.
The received message is "The URL does not reference an image file".
The only workaround I've found so far is to disable the image file check in the plugin source code.