A change to our logging may have caused users to see many "Preview" activities in their Updates feed. Usually these Preview actions will all show as occurring around the same time:
This is a known issue with our reporting in which thumbnail images of files are being registered as a Preview action. Each time you visit the "Updates" page, and more thumbnails are loaded, more Preview actions are logged.
Our Engineering Team is currently aware of the issue and working on fix. If you have further questions, please feel free to reach out to our User Services team by submitting a case.