The modular SRBs report a burntime of NaN and a thrust of zero in the VAB. RealFuels correctly assigns a fuel, so the engine configs might not be playing nice with Realfuels. Install is KSP 1.2.2, with RO and RP-0.

The RO SRB configs (which are 100% on RO's side) have been broken for a while. They need to be completely redone I suspect.

Copy that. Thanks for pointing me in the right direction. These SRBs are so nice I can't wait to use them!

If there are code-side changes needed in SSTU in order to make it all work, please let me know at that point. Would need to be quite specific as what needs changed/fixed though, preferably through a PR.

related: KSP-RO/RealismOverhaul#1625