Transferring videos from a Photos Album on MacBook Pro to iPhone

I am having difficulty transferring videos previously taken from my iPhone and then imported into Photos on my MacBook back onto my phone. I'll explain it step by step ...

1. I have imported various videos (and photos) taken on my iPhone into the Photos app on my MacBook.
2. Once imported, those videos and photos have then been deleted from the Camera Roll on my iPhone.
3. Within the photos app on my MacBook, I have then made various albums which often contain both videos and photos.
4. When i then re-sync my iPhone with iTunes on my MacBook, all of the albums I have created within the Photos app on the MacBook appear on my iPhone Photos app under the "From My Mac" section but when I go into those albums only the photos have transferred back to my iPhone and not the videos.
5. Accordingly, none of the videos saved into the Photos app on my MacBook are on my iPhone.

Finally, I do not have and do not want to use iCloud storage. Does anyone have any suggestions or know of a setting that I've perhaps accidentally turned on/off that would be causing only the photos and not the videos to transfer back to my iPhone?

PS. I swear that when I have done this in the past both the videos and photos from within the albums I've created have transferred back to my iPhone.

If of help, my MacBook is a 2012 Pro model running version 10.13.6 of Sierra and my iPhone is a 6s running iOS version 12.1.2.

Thank you for any help.