I was just travelling from the boathouse settlement when I noticed larger numbers of Settlers walking down the road, so I catch up to them and it appears to be every supply route guy I've set up all travelling together....this sort of explains the large number of sprinting Brahmin I have been running into since all but one settler was missing his Brahmin and the rest appear to be trying to catch up.

I just loaded it up to check at least sixteen settlers (they all moved of the road in two directions to fight wildlife and are moving about so its hard to get an accurate count) and now five Brahmin, so not every supply run guy just most of them......anybody else every seen this in game?

I've seen that, I have 7 caravans moving around near Red Rocket station.

No, but I had a Dr. from a first aid station in one settlement come up missing. then I get a need help with raiders quest from another settlement go talk to settler and none have the little green marker to talk to. So I look on map and it shows him wondering the wasteland. catch to him to start the quest and turns out to be my missing Dr.

Yeah I seen that as well as the Red Rocket is my main supply centre (with Sanctuary taking second place for linked supply runs), in this case though it that there were so many in a single group moving together that I was surprised, at first I thought it was a random event since one of them was a named NPC (the guy who gives you a sword), armed with a flamethrower, but then I realised who it was and then I knew that they were mine......shame as I thought I was getting a migration of new settlers.