Got the following error that caused me to have to restart my save:

The mod Rate Calculator Classic (3.0.2) caused a non-recoverable error.
Please report this error to the mod author.

Error while running event RateCalculatorClassic::on_player_selected_area (ID 55)
LuaEntityPrototype doesn't contain key stack.
stack traceback:
[C]: in function 'index'
__RateCalculatorClassic/scripts/inserter-calc.lua:81: in function 'inserter_calc'
RateCalculatorClassic/control.lua:189: in function <RateCalculatorClassic/control.lua:163>

How to replicate:
1. Drag rate calculator over entity and have the pop up box display.
2. Change the units drop-down menu to "Inserters".
3. Click on the units box.
4. Select any inserter.

Congrats, you just crashed your play session and now have to revert back to an autosave!

Thanks for the reproduction-instructions, this is fixed in the next release, although I don't know what it does (and it might be broken), but at least it doesn't crash anymore.

I have the same crash (Same steps, same error message) with mod version 3.0.4 in Factorio Space age 2.0.69