A story of ours was populated with story data from another customer

A user of ours was entering data, and suddenly the content of that data was populated with a message she did not write.

I am redacting the information here for security purposes, but it referenced a sharepoint wiki of a separate customer!

How was this data permitted to enter our project? If data from other customers is leaking into our project, what is happening to our missing data?

This is an urgent issue. How was this allowed to happen?

This was for Project 126287 and Story 69634