You need to clear the flophouse in order to establish the outpost. as long as the flophouse is not cleared you just can't proceed making an outpost no matter how high your viability score is. I guess you can't see the flophouse quest icon on your map and assumed you cleared it. My suggestion is to go back to the flophouse location and see if there are still enemies. If there are proceed to kill them and go to the house where you have to hold out until a hack is completed. Then go the building you couldn't enter previously. Clear out both the first and second floor and activate the switch at the end. The "Flophouse" side mission should be cleared now and you'll be able to put down the outpost. Hope it helps!
I had the same issue, left the planet came back, saved quit, then went back to the location, took a little bit to get the terminals worked out, for me they kept showing up as markers then, I would do one they would blink out, kept scanning & eventually it worked out. Was a pain though, like others I stumbled across it driving, the original hack just glitched out. Hope it helps.
Cheers
