Hi Jaap de Wit,
We apologize for the issues and the frustration this has caused you. Here at iThemes we value your feedback and are working hard to fix these pervading issues.
First, please make sure to keep the plugin as up to date as possible. Our developers are pushing regular updates to take care of bugs and have already resolved a great number of issues, and a newer version may fix the problem you are experiencing. If this does not work or you are experiencing a new issue, please fill out an iThemes Security Bug Report with as many relevant details as possible, so our developers can better address the issue.
We greatly appreciate your feedback and your patience in helping us resolve these issues as quickly and efficiently as possible.
Thanks,
D.V.