I updated to version 1.11.21 of this plugin last night. A few hours later my site went down with a 500 server error. Investigation revealed the issue to be a rogue "ess" at the end of my .htaccess file.
I deleted the corrupted .htaccess file and let WordPress generate a fresh one. Immediately it was being edited a few times a minute. Eventually the file became corrupted again, this time with mass repetition of the basic WordPress .htaccess code.
After disabling this plugin, the stream of constant .htaccess edits stopped. I'm not sure what was changed with the 5/31 update to version 1.11.21, but it obviously was not for the better.