My gut said, teeny tiny creepy crawly, super close to the lens, on it in fact, so totally out of focus, therefore no way to make out even tinier legs, etc. Blurred beyond all recognition, but yes, as Joel said, could easily be a part of a spiders web. Either way, it is something really close, and very small. Not such a big believer in the dust possibility in this case, because it’s too coincidental, two days in a row, almost exactly the same. Newly hatched batch of tiny spiders, wandering around, a possibility for sure.
One thing it isn’t, for sure, is ghosts, of any sort.