This was triggered with a basic operation of placing a heat exchanger. Initially it was right next to a fusion reactor but on a second launch of the game, I placed the heat exchanger by itself to trigger the same error. Logging this here before I start isolating mods that might be affecting it. Apologies if it's not related to your code, hopefully I'll have more debugging info for you soon. Since I know this operation has worked in the past (w/ and w/o SE), I'm guessing it's another mod interaction issue.

The mod Reactor Interface (2.1.1) caused a non-recoverable error.
Please report this error to the mod author.

Error while running event Reactor Interface::on_tick (ID 0)
Reactor Interface/control.lua:337: attempt to index local 'burner' (a nil value)
stack traceback:
Reactor Interface/control.lua:337: in function <Reactor Interface/control.lua:322>

Seems to be a problem with Reactor Interface, as the error says. Post it to their mod page, I'm not sure I can fix it myself.

Ack, forgot that was a separate mod I was testing and assumed "Reactor Interface" referred to something in RFP or SE. My mistake.