I noticed some likely unintended behavior when using RationalResourcesSquad in conjunction with Mk2Expansion and CryoTanks. Specifically the supplied RR_MoreTankSwitches.cfg which adds RR tanktypes to parts from the Mk2Expansion.
The issue stems from Mk2Expansion using B9PartSwitch transform keys inside the SUBTYPE nodes of a few parts that contain B9PartSwitch fuelswitch modules. This leads to selectable RR TankTypes without the needed transforms which causes a vanishing model when these tank types are selected in game.
Specifically the parts are M2X_Servicebay and M2X_UST. I'm fairly certain there aren't any other instances aside from these two, but with that being said I didn't manually verify this in the part cfgs of Mk2Expansion. So there may be additional instances?
I fiddled with modifying your supplied config in order assist with a fix, but the relevant patch in RR_MoreTankSwitches.cfg applies to many Mk2Expansion parts appropriately without issue, so perhaps a specific patch to these specific parts might be warranted. During the course of creating a temporary solution for myself I noticed that just using MM to simply copy the transform keys from the initial SUBTYPE leads to the potential for thematically questionable meshes being applied to certain tanktypes, e.g. clearly identifiable monopropellant tanks holding LOx. Luckily there are relevant mesh transforms included in the parts for the tank types added to these parts by RR. For both parts there is a base mesh or meshes necessary regardless of tank type, as well as supplemental transforms used to indicate the currently selected tank type. Relevant transforms provided below.
Lastly, and much less pertinent, both these parts include a "Monoprop" tanktype, which creates a redundancy when the relevant patch supplied in RR_MoreTankSwitches.cfg applies the base B9PartSwitch "MonoPropellant" tanktype.
