FWIW, might be helpful for others, not sure:
I was experiencing these same issues (blank white page on form submit, can’t access/edit forms in Admin dashboard). I tried a bunch of debugging of different things, but couldn’t figure anything out. For kicks, I went to the server logs because if you have PHP debugging enabled, PHP errors show up in the server logs. I found:
PHP Deprecated: preg_replace(): The /e modifier is deprecated, use preg_replace_callback instead in .../wp-content/plugins/wr-contactform/libraries/gadget/contactform-frontend.php on line 641
Removed some possibly sensitive info, but you get the point. It wasn’t a deprecation warning either, it was a deprecation error.
I was running version 1.1.11 of the plugin and wordpress 4.4.
I don’t know if that ultimately is the issue, but I gave up after a couple hours because these forms are mission critical for us. I moved over to Contact Form 7 and called it a day. The developer should be more responsible and state if they’re supporting the plugin or not.