The above two clips are from the New York Times in December 1944. It's not really clear what the source of the story is, and there's no actual eyewitness accounts. But the apparent similarity to the "orbs" reported by AARO, has led some to speculate they might be alien drones.
Then, as now, there was discussion on if they might be some sort of radar countermeasure. Manson W. Baldwin of the NYT wrote at the time (On Dec 15 1944)
Radar countermeasure balloons were used by Germany from at least 1943.
Deployed in September 1943, the Aphrodite was a three feet diameter sized balloon which floated above the surface and was anchored to the sea surface by a floating raft. The line was 50 meters long, three strips of aluminum foils were attached to the line to act as radar reflectors. The device had to be assembled on the upper deck, where the balloon was inflated with a hydrogen filled can. It had a lifespan of three to six hours after deployment.
That was not a silver ballon, but instead a balloon with strips of aluminum.
Interestingly, balloons were used as an offensive weapon by the British from 1942 to 1944, under Operation Outward.
Operation Outward was a British campaign of the Second World War that attacked Germany and German-occupied Europe with free-flying balloons. It made use of cheap, simple balloons filled with hydrogen and carrying either a trailing steel wire to damage high voltage power lines by producing a short circuit, or incendiary devices to start fires in fields, forests and heathland. A total of 99,142 Outward balloons were launched; about half carried incendiaries and half carried trailing wires.
However this seems to have ended on 4 September, 1944, so seems unlikely to be related.
Another possibility is simple barrage balloons. Although those are usually not spherical, and bombers would have been flying above barrage balloon height deliberately.
Does anyone have any other ideas?