This is usually a code error that comes to say that you are assigning an array of options that are not built correctly.
See here how options are suppose to be built.
https://www.wix.com/corvid/reference/$w.Gallery.html#ImageItem
For a basic way of doing images to gallery from dataset see here.
https://www.vorbly.com/Vorbly-Code/WIX-GALLERY-IMAGES-FROM-DATABASE