RKausS on "[Plugin: iThemes Security (formerly Better WP Security)] Theme Contact form no more works with iThemes enabled"

Hi
I've seen just now, that my theme contact page does no more work with Microsoft IE (does not send content), as soon I enable iThemes Sec. v4.6.10.
(Even ALL other plugins I use are disabled).
I tried around in the settings with some "suspect" options, but never with succes. I have really no more idea, which setting could cause this issue? I've tried around a lot! I even downgraded my theme to very early versions.
The only thing I KNOW is that with earlier versions of iThemes it worked very well.
Any hints for me?
Best regards,
Roman.

https://wordpress.org/plugins/better-wp-security/