New changes in Mac photos cannot be fully synced to iPhone via Finders

I've been manually syncing my mac photos to my iPhone from Finder (iTunes before) for years. For the past months, I found new changes cannot be fully synced to my iPhone manually. Sometimes I imported 10 photos and only 6 photos synced to my iphone via Finders no matter how many times I tried. This can be temporarily solved by reset my mac photos (option+command+click). Yet next time when I import some new photos, I have to reset Photos library again in order to sync all new changes via Finder. This is super annoying and I cannot find any more help than reset Photos library. Please support.