I think this is another issue. I update the RO to the latest release today, and the problem gone (When using the same LV which the issue came with) Yes, the propellants is right and fuel state is "very stable". I've tried to remove the overwrite of engine-ignitor in RP-0's cfg, then problem got fixed. But anyway, with the latest release of RO, everything works ! Add: I guess I unzipped one of RealFuels config file before. So ... May this cause the issue.