• Confirm you have an active Ring Protect Plan set up: Yes, the Basic Plan
• Confirm your snapshots were not deleted: Snapshots were untouched.
• Are all of you receiving the screenshot a neighbor previously attached? With a black screen saying 'This footage is unavaliable'? : Yes. In my case I activated this feature a week ago. Then my family noticed these spots in the timeline "This footage is unavailable"
I talked to customer service about this issue and was told it was because the software was updating. Unfortunatley for me, it just happened to occure while a package was delivered that was later stolen because I hadn't been notified it was delivered.