Could someone please explain the difference between instance and occurrence property with an example?
For a flat design there is no much differences. Occurrences can be used to store backannotation information that overrides properties on an instance.
For a complex hierarchy design you can have an instance present on one schematic page, that can have different RefDes depending of the hierarchical path. For situations like this you need Occurrences that are unique in hierarchy while instance might not be unique.
Hope this helps.