If I am importing files from my card reader and there are also new files in one of the watched folders to import, Photoshop Elements 2019 freezes. I have tried specifying Cancel on the window of watched folder import files and have also tried specifying Import. In both cases, the application freezes. I have to close PE and re-open. When I re-open the application it gives a message that there were new files imported and do I want to see them on the screen. When I say Yes, it then opens a window that says it is scanning for new files in teh watched folders. That process doesn't finish so I have to cancel it. Then I get to see the photos I was importing from my card reader. It, however, doesn't delete them from the card so I have to do that separately later.
Crash or freeze, Import and export, Organizer, Problem or error
I am not sure what your question is. Yes, watched folders can take up a lot of resources that may interfere with other operations such as starting a fresh import from card. Either you want folders to be watched or you don't. If you do, I suggest you allow the operation to complete before starting the fresh Import.
I also highly recommend NOT deleting from the card until you are sure the files have been safely stored on your computer. (And, personally, I do not delete from a card until the newly imported files have also been backed up.)