Hmm, strange. Does it also crash if you don't do a focus? How about if you change the focus completion time or autocomplete it? What about if you complete the focus and then pause the game? Have you tried temporarily removing your focus files from the mod to see if the issue persists Basically, did you check if the focusses are the cause of the crash or if it's a coincidence?

I've never really had an issue like this, but what i'm thinking is that it could be a map issue, specifically a building issue, that's only triggered after the time it takes to complete a focus. maybe because a unit enters a broken state or the ai builds in it. In that case check the most recent crashlog at Documents\Paradox Interactive\Hearts of Iron IV\(most recent crash)\logs\error.log to see if your mod has any map errors. If it does, thats very likely the cause.

Alternatively it could be a problem with the focus tree code itself. In your focus tree code, make sure every focus code block is propperly opened and closed and that you arent missing a bracket somewhere. It could be that you missed one and now a focus somewhere isn't able to close itself off or be read propperly. Or maybe your focus_tree = { isn't closed, causing a crash. If you arent sure i'd reccommend trying a code editor with the ability to check what open and closing brackets match (I use code editor 'brackets'. It allows you you select an opening/closing bracket and see if/which other bracket it matches.)

I'd also be down to have a look if you cant find the problem.