For some reason I had a Win10 crash, !?that happens a lot, and after that I get a lot of errors when I open the project I was running (UE4.24.3) - the problem is a missing file: ‘script\EnvironmentQueryEditor’ or something like that…
For some reason I can not find anyone reporting this kind of error, and I spent 2 hours trying to figure out what went wrong! So I post this to save you some time
Solution What happened was that the editor preferences was lost… I can not tell why, but for some reason these are not saved/backed up… you could save them, but when you try there is a good chance that you will overwrite some other config. The suggested name for the exported file: Appearance Backup 2020-04-02 160716 - well as they say in Westworld: “that looks like nothing to me”. 
In my case the experimental setting for AI (EQS) was lost - however I can not see that I changed that, or anything else. from the default, so I guess that many other settings can be lost?
Suggestion for the editor pref. etc.: There is a “Favorite” option, you can set when you change something - that is clever, if you even know about it - but why not simply always have a backup as well as a show/reset to default values?
I don’t know if there is a clever way of reporting such “missing/lost” editor options… but perhaps the assets that depend upon them could hold meta-data with a reference to options/plugins etc…?