If you know which 8 pictures these are, try exporting them, and then re-importing them. Corruption in pictures can cause interruptions in the whole process, and it's good to find those pictures and fix them.
I'm not sure what you mean by " run the duplicate search." There is no option to start a search-- Photos does that once for each picture as it's imported. Some pictures will appear as duplicates to us, but may not be counted as duplicates to Photos-- perhaps the metadata, resolution, file size, etc might be different. There are other Duplicate finders, some of which really mess up the Photos Library. We know that the trusted 3rd party app PowerPhotos ($40,) which does way more that duplicates, is safe. PhotoSweeper ($15) is focueed only on duplicates, it's cheaper, and it offers great options--I'm pretty impressed by it. But I really just depend on Photos.
Many operations use the Mac's empty storage space to move files around. If you run out of storage, then those operations may not be able to be completed and, ironically, that can mean that even deleting doesn't work. If you have less than 10% available, then things can get lost forever. My 1TB MacAir started doing crazy stuff with 125GB free, and it cleared up when I got to 150GB free, so I keep at least 15% free on my Mac.
It's not clear to me what Mac you use. A portable Mac shouldn't keep the Photos Library on an external drive--plugging and unplugging the drive can be very confusing for Photos, since it does so much in the background. But for a desktop Mac, an external drive is fine.
For a limited storage MacBook, Optimized iCloud Storage is a good choice, though you need to keep a backup on an external drive.
Backup iCloud Photos from an Optimized Mac - Apple Community
A Mac can have multiple Libraries, so many of us keep are Favorites on the System Drive to synchronize with iCloud, and we have archive Libraries on external drives to keep the rest of the pictures. We use the trusted 3rd party app PowerPhotos ($40) to keep the multiple Libraries organized.
Let us know how it goes…
