We found an important regression in XWiki 15.10.3 and XWiki 15.10.4 on the migration we provided to clean up the notification filters. This regression impacts the notification filters created for pages in subwikis: those are lost when the migration is performed.
We advise any administrator who hasn't performed the upgrade yet, to postpone it until further notice as there is a risk of data loss. We will provide information soon to Administrators who already performed the upgrade on the possibility to recover the lost filters from database backups.
There is no possibility of recovery without backups: instances already migrated without database backups have entirely lost the filters for subwiki pages.
[Edit from the 17/01: XWiki 15.10.5 has been released which fixes the regression. A recovery procedure has been posted to explain how to recover data from backup.]
