I've been relying on the Trim Empty Lines in Posts to successfully remove empty <p></p> in posts on our forum. However I've had to disable and re-enable it a few times in order to troubleshoot other issues (the Invision Community team asks us to disable all 3rd party plug-ins to troubleshoot issues) and since the last time I've re-enabled it I notice it isn't working, I can still see empty <p></p> displayed in posts.
I'm not sure if this issue started with v4.7.15 or before that as I had left the plug-in disabled for a while.