OK, that means that you do have the capitalisation problem. Basically, what happens is that you have two different folders, one called ‘MY LIGHTROOM PHOTOS’ and the other one called ‘My Lightroom Photos’. In other words, the names are the same, except for the capitalisation. Because MacOS and Windows are case-insensitive, your OS sees those two folders as one and the same folder and so it deals with this without you even being aware of it. You will only see one version. But Lightroom is case-sensitive, so Lightroom does see two different folders.
Here's how to fix the problem. Because you do not see the ‘My Lightroom Photos’ folder in Lightroom, you will have to solve this at the subfolder level. Follow these steps carefully. Try it with one subfolder. If it works, repeat steps 3 - 5 with the other subfolders.
1. Backup your catalog.
2. Create a folder directly on the root of your internal hard drive, call it whatever you want, say "Capitals Fix". Note: do this in Windows Explorer/Macintosh Finder, not in Lightroom.
3. Right-click on the one of the problem subfolders in the Lightroom Folders Panel and select "Update Folder Location". In the file browser that then opens, browse to and select the "Capitals Fix" folder.
4. Don't be alarmed as the subfolder will disappear from the Folders Panel, "Capitals Fix" will appear but all the sub-sub-folders that were listed under the original subfolder will now have "?" marks.
5. Now right-click on "Capitals Fix" in the Folders Panel, and again choose “Update Folder Location". This time browse to and select the original subfolder inside MY LIGHTROOM PHOTOS. You may get a "Merge" dialog box, select "Merge" and everything should resolve itself.