the 14393 build is not what you get from WDRT (I have DS unlocked, RM-1118). I did that yesterday, and it was 10586 that it installed. I then upgraded through Insider Slow Ring, and received 14393.
When it had gone through multiple incremental updates, I did not have double tap, even though the last one was 14393. After the above rollback and one-time update, coupled with a hard reset, I do in fact now have it.
It almost weird getting used to double tap again, but it sure is nice. Double tap to wake, and double tap on nav bar to turn off the screen - two nice features that require looking for the power button, which is especially nice if you have a case.
Glad to see this feature back.