On my first character, I noticed that Jamaica Plains was always getting more settlers as time went on. At first it only had 3, then I go off questing for a bit, then when I check my Workshops page I see it's at 16 settlers. I move settlers out until it's down to 5, go back questing, only to find it's back up at 16 again a few hours later. It was the only that settlement was getting infinite settlers no many how many I moved out.

Didn't have this happen on my second or third character, but now on my fourth I'm having it happened again. This time at Graygarden. I'm now at 3 settlements with max settlers (16 with Charisma) due to emptying Graygarden out of human settlers multiple times, but no matter times I empty it there's always new settlers showing up.

Is anyone else getting this?

Have you tried deactivating the radio beacon? I have had a few (like Tenpines) reach about 16 or so settlers and can't fit any more in without a redesign so I turned off the beacon in those places and the populations have remained constant.

As for why it's only one or two particular settlements is anyone's guess. Bug, maybe.