Mailster has been tested thoroughly and follows the WordPress Coding Standards. This means it should work with every plugin or theme which also follows those standards. If you experience any issue it’s often caused by a third-party plugin or your current theme.
To make sure it’s not a bug in Mailster please try to replicate the issue on our demo first. If you cannot repeat it there it’s most likely a problem on your site only.
Here’s a quick video to help troubleshoot this kind of problem.
Health Check Plugin
Another option is to use the official Health Check & Troubleshooting plugin from the WordPress repo. Please follow the official guide.