Rereading your original post I see several things:
1) "No bang, just Poof. There was a good deal of un-burned powder(flakes, like right out of jug) left in the cylinder chamber, cylinder face and forcing cone."
Simple logic says the primer ignited. If not the bullet would not have moved and you wouldn't have had powder everywhere. Possibility of the primer being faulty is very slim, although it is possible. You can try a different brand primer if you can find them.
2) "I'm absolutely certain there was powder in the case because I've pulled every case out of the shell holder to visually confirm powder was dumped before seating the bullets."
Good safety check. Doesn't mean you didn't have a light or heavy drop in some cases. Personally I weigh every charge, but I am OCD about some things. A light powder charge may have caused a squib, but most likely would not have left a "good deal of un-burned powder" as you described.
3) "I've been placing the primers in the primer arm with my fingers rather than the feeder. I've read that can lead to contaminating the primers."
This is possible but unlikely. I wear nitrile gloves while reloading, to keep my hands clean and not contaminate any components, and I also place every primer in the primer arm. Primers are pretty tough, and last a long time according to my research.
4) "Last night I decided to see how these rounds chambered in the cylinder and they were slightly difficult to load. The case lip where it meets the bullet seemed to need more crimp (lee fcd) so I ran the through the crimp die again after adjusting it tighter."
"Slightly difficult to load" indicates to me that you may need more crimp, OR that your cylinders may be crudded up and need a good cleaning. I have no experience with the Lee FCD so I can't/won't comment on that. I roll crimp all my 38spcl and 357mag rounds into the cannelure.
I still believe, although I may be wrong, that you had a pressure issue (not enough).
I said you may need more crimp, but you may need more neck tension also. Your sizing die may not be screwed down enough combined with not enough crimp, leading to your bullet starting to move out of the brass before the powder ignites completely. In basic terms, enough pressure to start the bullet moving, but not enough to push it completely out of the barrel or get a complete burn of the powder, leaving un-burned powder as you described.
FWIW, for 38spc I run 3.9gr of W-231 (same as HP-38) under a 158gr sjsp (semi jacketed soft point) through a 6" barrel and have no issues. Your bullet is plated vs. my jacketed, but I don't feel your load is too light.
chris