Additionally, the "All Photos" number is about 1,100 greater than the sum of photos in the various albums.
Additionally, the "All Photos" number is about 1,100 greater than the sum of photos in the various albums.
By @bfilipiak
What that means is that there are around 1100 images that are in the cloud but which are not allocated to any album, which is not untypical. Albums are simply virtual containers, so images can be assigned to one or more albums....or none.
So the first thing to try to establish is if any of your "missing" photos are still in your cloud storage (but not assigned to any albums), or are actually not in your cloud library. Open the LrWeb app in a browser window and check the number of images in All Photos, is it the same as the total in All Photos in the Lightroom Desktop app? If so, and there isn't a Sync Errors album in the LrWeb app (it would be shown just below All Photos), then stuck syncing likely isn't the problem.
In which case, to check if any of those 1100 images in All Photos include your "missing" photos, start with an album where you think some images are missing, find an image that was taken on the same day, check the capture date, then in the Lightroom Desktop app use the Date filter and select that date. That will then display all the images in the library which were captured on that date, examine the result to see if any of the "missing" images show up. Let us know what you discover.