This step was completely unnecessary and also completely wrong. Furthermore, if you really re-imported the images, you shouldn't have any collections and you shouldn't have greyed out images in collections.
So what did you actually do? Can you tell us step-by-step what you did from after you re-installed LrC until you found the folders populated and the collections greyed out? Can you show us a screen capture of (one of) your collections?
A few months ago, because of storage space issues, I moved all my photos from my internal drive to an external drive.
I then had to add the folder on the external drive to LR, and back then had to import the pics into LR. [I had read something about just re-pointing LR to the new folder, but I could not make it work.]
This time, after reinstalling, the LR folders list did not include the folder on the external drive. So I again had to add the external drive folder to LR, and again had to import the pics. It took a few hours.
I had attached to my first post a screenshot of one of my collections. I'm attaching it again. And I added a second screenshot, showing in the folder tree the photo that is highlighted-grayed-out in the collection screenshot. To show that the photo is there, just not showing up in the collection.