I tried at Best Buy tonight, and no dice. The employee was all ready to scan the gc, no issues from him whatsoever, but it was the computer that rejected the purchase. So it seems it's on a corporate level. I didn't think to try to buy something else with it, but I always buy an amount above the BB gc and pay the rest out of pocket, and no dice.
Also, a friend of mine tried at Walmart about 3 days ago and no dice there either. She tried to purchase a Disney gc along with another item using Walmart Pay with gcs loaded in there. The register deducted the amount of the other item from Walmart Pay, and was told she owed the rest. I don't know if Sam's Club is doing the same or not yet.