I'm sorry, but I didn't take the time to read all of these posts. However, I do have a good solution that works.
I don't play this style, I been using finger picks all these years and haven't explored flat picks too much. On occasion, even my finger picks work themselves loose. Try a rosin bag, like the stuff that rock climbers, bowlers, baseball, golf, and tennis players use.
Before you start to play dip your fingers, the ones that you'll be holding your picks with, in the rosin powder. The rosin will react with your body heat and make your finger tips tacky and better able to hang on to your pick. While you're at it, you can also dust your pick with the stuff. I think they even make it in different grades of stickiness. Like the different grades of cake rosin that violin or upright bass players use.
The company that makes the stuff I have is called Forrest Enterprises Inc. They're located in Piqua, Ohio 45356. They also make another product called Mor Grip.
There is also a liquid that's used in theater productions to attach false facial hair etc. It's called spirit gum. It's a mild contact cement. It's sticky enough to hold but not as strong or as toxic as the industrial strength version of the stuff that you might find in your average hardware store. This stuff dries quickly and leaves your fingers tacky enough to help your picks to stay where they're supposed to stay.
Try either of these and you should have no trouble, but if you find that one or the other isn't enough try using both together. I have had to this and found this answer to be the perfect solution to slippery picks.