Indeed, I was able to re-create the issue. It is caused by a malfunctioning fallback checking method, it goes into an inifinite loop whenever internet explorer 8 or lower UA string is detected.
To solve it temporarily, replace the wp-content\plugins\ajax-search-pro\includes\classes\filters\class-asp-formoverride.php file contents on your server with this: https://goo.gl/w4cTYD
That should do the trick.
I will of course include a fix in the next release.Best,
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