Cant access the "excavated site" area

Hi

i beat the act 4 story boss late last night in "the excavation" area, and went to bed without going to the next area, it think its supposed to be the "excavated site", when i got back on today the boss appeared said the line when you defeat him and just disappeared, the door to the next area won't open and i haven't unlocked the teleporter to be able to access it.

can you unlock the teleporter to the next area so I can warp to it?

the troubleshooting i tried was
warping to act 4 hub and back - didn't work
restarting the game - didn't work
teleporting using checkpoints in the area - didn't work

also, unrelated to the above problem, in the "plunderers point" area also in act 4 i did the tutorial for the explosives but i didn't blow up any flags, now that i have come back all the flags are gone, the island minimap is already lit up and there are no enemies spawning on the island, i also have no other quest for the island. im not sure if this is a bug or i need to find something specific on the island

thanks

an update to this,
i just kept restarting the game, i cleared the area again, the boss reappeared and after i killed him again the door opened