See here:
Kerbalism/Kerbalism#221

It's weird, but at the end the removal of these mod folders solved the issue:
InterstellarHybridRocketry
WarpPlugin
TweakScale\

I tried it first by removing these folders, but that didn't work:
PhotonSail
RealHeat
SolarSailNavigator\

Can you try:

• Kerbalism and TweakScale only
• Kerbalism and Interstellar Extended only

Including dependencies in both cases for installed mods

I would have to reproduce that particular issue, which was a vessel in orbit had no more EC as resource in the persistent file after I added KSP-IE - which made Kerbalism throw exceptions.

After removing KSP-IE and TweakScale, the vessel still had no EC in the persistent file, but Kerbalism no more threw exceptions and after loading that vessel in flight mode it was "repaired", so afterwards it also had EC as a resource in the persistent file.

See Kerbalism/Kerbalism#221 (comment)

This comment and the following could™ describe the reason:
Kerbalism/Kerbalism#221 (comment)