On a previous mission, I had landed a vessel on Duna.
Now, when I build a vessel in the VAB and launch it, KSP hangs on a loading screen while in the background I hear a series of crashing noises which eventually die out. The hang continues for some time, but I left KSP in the background and checked it after several hours, and it turns out the new vehicle had spawned on top of the vessel on Duna!
Screenshot below: this craft file included launch clamps which you can see extend to the top of the screen (though the bug happens regardless of which craft file I use or which launch site I choose).
System Details
KSP Version: 0.1.0.0.20892
Operating System: Windows 10
CPU: AMD 5800X3D
GPU: NVIDIA RTX 2070 Super
GPU Driver Version 528.49
RAM: 32GB
I can share the save file if requested. To reproduce, I load the save, open a craft in the VAB, and launch it.