Simulink coder error - Empty code

Hello. I'm trying to generate the code from a Simulink model, which is using PLECS Blockset as well, to run on an OPAL-RT RTS. The model is running completely fine on its own, however when I try to compile into C code I get the following error:

Error: Simulink Coder Error in block: "two_cell_inside_module/Circuit/ S-Function ", block type "S-Function": Fatal error during code generation: Empty code in Circuit/Phase A converters/CHBA1/MFB1/Sub-cycle average

It seems like this error appears for a number of different blocks in the circuit model. Does anyone know what is causing this problem and how I can fix it? I'll also attach the full model, if someone wants to have a look.