It happens to me too, when entering the Vulcan City my plot failed to load then when going out to vc all of my vulcs became missing so I have no choice but to log out and re log in the game.

I am seeing this too with lost plot information. I am forced to relogin in order to get them back. My issue does not seem related to Vulcan City. It seems to happen intermittently, sometimes after being logged in for only a short while.