My play-through went until I had four outposts (Red Rocket, Starlight Drive-In, Hangman's Alley, and Taffington Boathouse) supported through IDEK warehouses by three normal settlements (Sanctuary Hills, Abernathy Farms, and Ten Pines Bluff). I had turned off soldier requirements because I could never get any increase in food availability for recruitment, even though I had a large excess in crops as seen by the IDEK warehouses. After I got a message saying that morale was higher because of an especially good result when taking Taffington Boathouse from the Gunners, I went to read up on Morale and Control. When I came back to try distributing my Warriors among my outposts, I discovered that most of them had turned into Workers and I could no longer alter anyone's roles. I am not sure when this change occurred. I came to this forum and found a thread where people were discussing being unable to change roles, and a possible connection with Settlers appearing among the Civilians. I do have those. I did not see any conclusive solution, so I once again set aside the play-through.
One note, after I took Starlight Drive-In as an outpost, I was able to access the workshop. Then one of the Civilians came to me and asked me to wipe out raiders at Walden's Pond. I did that, and they agreed to join the Minutemen. The game still sees Starlight Drive-In as an outpost, but I do not know if it also sees it as a normal settlement. That may be where the Settlers came from? I do not recall seeing a Settler before that, but it was very shortly after the conquest when the Civilian approached me so I had not looked at everyone.
Also, every time I entered Starlight Drive-In, visitors run out of the settlement. One or more visitors inside the settlement are screaming and begging for help, but I never find any visitor inside either dead or tied up. The screaming stops fairly soon. I am not sure what event is being triggered by my entrance into the settlement, but it is not pleasant.