Please refer the below article for correct workflow to create destination folders and sub folders.
Let us know if that helps.
I have been importing images forever without a problem. I undertand folders and subfolders, I have turned off all file handling,presets etec. I search around in preferences but could not locate anything causing this. The subfoldere that is created is named the same as a destination folder created months ago (could it have properties that cause this?)
You can try restoring the Lightroom Preferences back to restore and check if that makes any better.
I solved the problem. I think this should be addressed.
When importing there is no facility for "putting in sub-folder when
showing all options. But there is lower left bottom a little box that
when hovered says "show less options". When that window opens and copy
is selected, it gives the option to put into a sub-folder. That was
selected and causing the problem.
It is an option that should show in the full screen as well as the show