Elements Organizer 2018 - missing photos in the Catalog

Hi,

I have one folder on my hard drive which contains all my photos (it's a folder synced with the Google drive). This folder is set as a Watch folder so all photos in it should be available in my Catalog (I have only one Catalog). Unfortunately, it's not true.

I know that folder contains five photos with names starting "IMG_20171226_1836" (this is what I see in the windows explorer). However, If I try to search for these photos in my Organizer Catalog using the exact same name, only two photos shows up.

Reconnecting missing files (File -> Reconnect -> All Missing Files) does not help, it says "There are no missing files to reconnect".

The only solution which works for me is adding missing photos to the Catalog manually (Import -> From Files and Folders...). But this solution is not usable because I have more than 1000 photos so I can't compare what is missing.

Creating the Catalog from the scratch it's not an option because I already added many faces, places, tags... Also, how should I know that even after that all photos will be added to the new Catalog?

Any ideas what the problem could be?

Any help would be really appreciated!

Thank you.