After loading my 1.1 save in 2.0 and simply waiting a few seconds (mods doing background update stuff too), I get this error:

The mod Circuit Visualizer (2.0.2) caused a non-recoverable error.
Please report this error to the mod author.

Error while running event circuit_visualizer::on_tick (ID 0)
__circuit_visualizer__/control.lua:324: attempt to index field '?' (a number value)
stack traceback:
    __circuit_visualizer__/control.lua:324: in function 'visualize_entity'
    __circuit_visualizer__/control.lua:417: in function 'update'
    __circuit_visualizer__/control.lua:720: in function 'on_tick'
    __circuit_visualizer__/control.lua:807: in function <__circuit_visualizer__/control.lua:803>

This does not happen in another save that is from the same playthrough but a couple dozen hours earlier (I think).