I'm seeing the same problem. With the addition that even if the reactor is on top the units won't work unless connected directly to an Interstellar part (Science lab, etc). Edit: For additional information, resources like Waste Heat and Electric Charge seem to be transferred correctly across entire vessels while the reactor thermal load is not transmitted to attached parts. Deletion and Reinstall of Interstellar has no effect. All mods with plugin components were also removed with no effect. 2nd Edit: I just realized xchoo was talking about multiple reactor/gen combos. The problem I described is with only one reactor/genset per ship.