I updated this morning to the latest version of UELI and in this version I can't see any folders when I type the name of them (same name that I used to type to find them). I tried re-starting the plugin but it didn't help.
Can you show me the simple folder search settings you've made in the settings window?

Is there a hint in the debug log?
Here is how you open the debug log:

Will check, sorry for the late reply
I can't see anything about folders in the error log. The only error I see is this "2019-09-17T13:28:20.516Z error: stdout maxBuffer length exceeded", which I assume has nothing to do with folders?
This is exactly the issue. I'm looking into it asap!
Added a fix for this (included in the next release). The problem was that your file search tries to index alot of files (probably because one of your folders is searched recursively). I added a limit of 1000 files which fixed this issue but probably leads to files and folders which can't be found anymore. I suggest not using the recursive file scan too often. If you have big folders to be searched I suggest using the everything plugin.