Look out for images that have been added to a set above the correct one, such as the 2017 set instead of the correct Gallery set inside it.
Troubleshooting - Image uploaded, but can’t be seen on the site
If you can't see an image on the site, the first thing to check is that it's in the correct set.
Make sure that you're checking the testing address of your website, or it may be cached.
Use the Sets panel on the review screen to check that the image is in the correct set.
You should also check the time the image was taken. An incorrect camera date or time could show images out of order in a gallery sorted chronologically.
If this is the case, you can shift the Exif time of any affected images.
If this is the case, you can shift the Exif time of any affected images.