I've played KSP for years, currently on version 1.11.0.3045 w/no mods. I wanted to start a new, Career, game. Started okay, but after my first mission, when I obtained fuel and engines, I tried adding an FL-T100 Fuel to a MK1 Command capsule. The fuel tank disappeared and the game froze, I couldn't even exit until I clicked 'New', then exit.
I resumed and with more missions using the RT-5 Flea, I acquired additional fuel options. I tried the FL-T200, but same problem. Oddly, I can start with a fuel tank and add a capsule, then re-root to the capsule, but adding a 2nd fuel tank (it disappears) causes the game to freeze.
Any advise would be appreciated.
Thanks, David