If you are here, that is probably because you got this: Got an error from WP. Please check your PHP logs (on server) and WP/LR logs (on your computer).
First, make sure your checked your logs (there is a WPLRSync.log in your Document folder and the PHP error logs are located on your server – you can ask your hosting service since they all host those differently). If there is specific error message, then the issue can be obvious and resolved very easily. Otherwise, it is definitely (at 99%) an issue with XML/RPC communication.
There mainly are two types of XML/RPC related errors. The ones that always happen or happen randomly (blacklisting) and the ones that happen always with exactly the same files (PHP Errors).
In most cases, WP/LR Sync connection related issues are linked to the fact that XML/RPC requests get blocked by the hosting service; this is usually automatic and supposed to protect your website from malicious attacks. This security measure is not required anymore but cheap hosting services prefer to keep this one just to avoid any kind of issue.
You can attempt different things to resolve this issue:
1. Talk with your hosting service about it. It is the best to do. Contact them, give them your IP address, explain them that you are using WP/LR Sync that keeps your Lightroom synchronized with your WordPress through XML/RPC. You would like to be either remove from the blacklist or added to the whitelist. You can also mention that the User Agent used by the Lightroom plugin is “WP/LR Sync”, they can whitelist on this as well.
2. Set-up a ‘Delay’ in the WP/LR Sync service options. XML/RPC requests are often blocked because they are too fast. Set-it up to 30 seconds, it should do the trick. Please note that if you have already been banned or blocked from using XML/RPC, that setting will do nothing. You might have to wait for a while before being able to do a request again.
3. Rename the file “xmlrpc.php” to something else (“xmlrpc-wplr.php” for example) at the root of your WordPress install. Then, in the WP/LR Sync options (see above), change the XML/RPC handler to that new filename.
It is not exactly a XML/RPC error even though it might appear like one. If always the same files don’t get uploaded then it means the generated files for those images are too big and get a timeout on the WordPress side or the memory is not set high enough in you PHP config.