OTA Channels Oddity

I'm in Rhode Island and this morning none of my Boston channels were coming in. I did a rescan and ended up with some of those channels doubled (5.1, 5.1, 5.2, 5.2). Ok, seen this before.....new frequency, not exactly. Boston stations still out, but now the doubled number is pulling New York channels with great signal. ?????????? About an hour later, most of the Boston channels are back with the associated NY channels no longer coming in. The Boston channels that are still missing, still have NY channels. (FYI, diff. freq.)