Quite a puzzle.
So on two different Star machines, loading two different calibers (.38 Spl & .45 ACP), two different powder magazine materials (alum & plastic), two different powders (WST & Bullseye), made by two different manufacturers (Hodgdon & Alliant) - complete powder flow stoppage occurred during a reloading session.
Given the level of experience you indicate, nearly all questions posed will seem simplistic and insulting, but are not intended that way.
Did the stoppage/blockage occur in the magazine or the spout? Are you using the large spout?
The Star system has the "clicks" to slightly vibrate the powder bar. Are the rollers on the back of the charge bar rolling freely?
In your last example, a factory-fresh, sealed, 1 lb. can of BE is opened, poured into the powder magazine and then loading commences until sometime in the first 45 minutes the powder bridges/stops flowing. It would have to be something within the physical powder delivery system of the Star. Maybe simple stuff like spiders, cobwebs, oil, moisture, etc. Since you've used these machines extensively with success, it's hard to understand how they would suddenly become so super-static charged as to completely halt the powder flow. Maybe empty out the magazines and vigorously blow them out with dry compressed air, particularly the baffle areas. Then swab out with something that evaporates and leaves no film like denatured alcohol, then blow out again. Clean the charge bar, powder housing, and spout with the same stuff. Everything in the world of powder on the Star ends up dry & clean.
Just "spit-balling" here. A very frustrating issue to resolve, I'm sure.
Thoughts from others??