Welcome to SRP. From your description it sounds as if you know what you are doing and have plenty of experience. The first thing I think of is very coarse whiskers and the second is skin stretching being inadequate. From your description of the razors passing HHT and easily popping arm hair, not pulling on the passes subsequent to the first WTG, it sounds like they are sharp enough.

You will think I am crazy or kidding but I am serious. Try doing your preparation and your shave with cold water. The theory is that the hot water softens the hair making it more difficult for the razor to cut it. The cold water leaves the hair stiff and the edge cuts more efficiently. This has proven to be true for me and I only prep and shave with cold water for months now. Go to this thread here for a more complete explanation.