The specific error seems to be:
Error while loading entity prototype "negative-space-auto-thermal-interface3" (reactor): Invalid heat pipe connections: connections must all be at least 1 tile distance from each other. Connection 1 ends up being the same as connection 5. in property tree at ROOT.reactor.negative-space-auto-thermal-interface3.heat_buffer.connections
This happens with only Heat Management installed.
It looks like TFMG-thermal is attempting to create a heat interface for my auto-generated negative space entity because Heat Management asked it to.
I think this is clearly a bug with Heat Management. I'll move this issue over to that mod.