I'm getting a similar error: USSolarSwitch.GetModuleMass, CurrentSelection: 0
This completely breaks Delta-V calculation (every stage shows as 0m/s), although it shows up fine in VAB. Only happens if I use the Advanced Sub-Satellite, but I suppose there are other parts causing this issue too.
I'm running KSP 1.12.4, mod version is 4.0.0.8.