If a category is moved:
example - "Photography" category moved :
old location: "All categories > Other collections> Photography"
new location: "All categories > Photography".
The favourite you had set on "All categories > Other collections > Photography" becomes obsolete and redirects to a page with all the items of the website.
If a category is deleted :
example - "Plants, Seeds and Bulbs" category deleted :
before deletion: "All categories > Other collections > Plants, Seeds & Bulbs"
items transferred to: "All categories > Other themes & collections > Unclassified".
The items in this category are transferred to a replacement category.
The favourite you had set on the deleted category "Plants, Seeds and Bulbs" becomes obsolete and redirects to a page with all the items of the website.
In either case, we invite you to delete your old favourite list and create a new one.
More information in these articles:
Add or delete an email alert for a favourite