Thanks for using the Apple Support Communities.
I understand that when you enabled iCloud Library to sync on your iPhone 7, Live Photos have disappeared. I'll be glad to help you try and retrieve these Live Photos.
First, I recommend trying to search your iPhone to try and locate these Live Photos: Use Search on your iPhone, iPad, or iPod touch .
Next, have you ever backed up your iPhone to iCloud or iTunes? If so, you can try to restore from a backup to get these photos back: Restore your iPhone, iPad, or iPod touch from a backup .
Please let me know if this helps, or if you have any questions.
Best Regards.