Your problem was like unto mine ... type of footage mattered not at all. As has been reported by others here. I had mov, mp4, and AVCHD from PrPro sequences that wouldn't work in a DL mode ... an immediate "crash" of utilization of the video card, and then an ability only to limp along without it in a DL process. I could go to a "native" Sg workflow, with the mov coming directly into Sg, or re-work some Cineon footage I'd exported out of Sg earlier, and it worked in GPU mode happily.
So ... it would seem to mostly be a situation of the "extra" precaution added to Sg in the DL mode included in the last update. That at least is the "working assumption" that I've been able to find. And of course ... we all hope we get a total fix of this ... soon ...
neil