When using https://mods.factorio.com/mod/circuitissimo, I get this error when exiting the circuit. I believe circuitissimo removes the surface when it is done.

120.412 Script @PowerOverload/control.lua:271: Creating transformer surface circuitchip_1-transformer

[Do work in circuitissimo]

134.352 Error MainLoop.cpp:1284: Exception at tick 4244678: The mod Power Overload (1.1.6) caused a non-recoverable error.
Please report this error to the mod author.

Error while running event PowerOverload::on_surface_deleted (ID 64)
PowerOverload/control.lua:286: attempt to index local 'surface' (a nil value)
stack traceback:
PowerOverload/control.lua:286: in function <PowerOverload/control.lua:284>
172.270 Info HttpSharedState.cpp:54: Downloading https://mods.factorio.com/api/mods?page_size=max&full=True&version=1.1.59&lang=en

Thanks for reporting this - it was a bug inside my code that handled surface deletion. It looks like you're first to run Power Overload with a mod that deletes surfaces!

Fixed in v1.1.7.

I confirm it's fixed. Thank you for the quick turnaround!

Great! I've been doing a lot of work on Power Overload this week so you caught me at a good time! Some useful improvements will be coming in the next week or so...

Can't wait =)