Hi jocelyne259,
Thanks for using Apple Support Communities. It's possible that you don't have enough storage for the additional photos. Please review the following:
"The number of photos stored on your Apple Watch depends on available space. To save space for songs or other content, you can limit the number of photos stored on it.
- Open the Apple Watch app on your iPhone.
- Tap My Watch, then go to Photos > Photos Limit.
To see how many photos are on your Apple Watch, do one of the following:
- Open the Settings app
on your Apple Watch, then go to General > About. - Open the Apple Watch app on your iPhone, tap My Watch, then go to General > About.
To see how much space is used for your photos, open the Settings app
on your Apple Watch, then go to General > Storage. To do this on your iPhone, open the Apple Watch app, tap My Watch, then go to General > Storage."
Choose a photo album and manage storage on Apple Watch
Let us know the results. Be sure to include any other troubleshooting steps that you may have tried.
Have a great day!