I got a load of new migrants and was assigning them jobs while chasing down skeletal rhesus macaque with my military. This was the first migrant wave and I was still living out of the wagon and my dwarves idled on the surface.
I assigned a load of jobs in my workshops (new doors, beds, etc) and all the jobs cancel by themselves with no announcement. I notice two of my miners are starving/dehydrated and this is when I noticed the strangest part.
The miners could do anything underground if I set them the labour, however they won't use items on the surface, they can still travel to the surface. This means they won't eat/drink and will die, if this happens it's over as I'm pretty sure the surface dwellers won't retrieve the picks and I won't be able to dig anymore. Now the people on the surface are the opposite, they will interact with things on the surface but are refusing to use anything underground. Movement is fine, I can station people anywhere. I've checked burrows and priority settings and they're all empty.
What's suddenly caused a split between my 2 miners and everybody else? It's like controlling two fortresses at once which is rather annoying as only two dwarves have access to my fortress but no supplies.
Edit: I'll note that I added four more stairwells in new places. I even dug out a fresh section, connected it to the surface, then to the fortress. Nothing. I even tried ramps incase stairs were being weird... Nothing.