Splitters in the latest experimental version of the game can be connected to circuit network, this mod causes a crash when opening a splitter that's connected.

Was just about to report this. The error is:

The mod Filter Helper (0.2.20) caused a non-recoverable error.
Please report this error to the mod author.

Error while running event FilterHelper::on_gui_opened (ID 101)
LuaSplitterControlBehavior doesn't contain key type.
stack traceback:
[C]: in function 'index'
__FilterHelper/control.lua:450: in function 'add_items_circuit'
FilterHelper/control.lua:525: in function 'add_items'
FilterHelper/control.lua:556: in function 'update_ui'
FilterHelper/control.lua:595: in function <FilterHelper/control.lua:590>

+1

This looks like a basegame bug to me, made a bug report: https://forums.factorio.com/viewtopic.php?t=130978

Thanks for the report. I'll check it out.

Indeed looks like an issue in the game, and will be fixed by version 2.0.68.

Should be fixed now on the experimental branch.

I can confirm, works with 2.0.68 for me.