My Admin Notification emails also were not showing up.
Some sloppy programming in pie-register.php between lines 1356 and 1370. A lot of mixing of double quotes and single quotes. I think the ultimate problem is the single quotes around one of the carriage return new line thingies. You have to use double quotes.
Not harmful but still perplexing is the inconsistent uses of concantenation and curly quotes. Pick one or the other and stick with it.
It also seems that a reliance on CKEditor in other areas of the program is misplaced. CKEditor seems to have stopped working in WordPress 4.0 and is no longer, apparently, supported. The “Replacement Keys” feature is rather unclear, anyway, and would be better implemented as a simple text explanation, ie., use “%user_name%” where you want the user name.
Otherwise, marvelous job.