Hi all, For the last 2 months the app is not creating the recurrences of any of the activities.

It looks like auto-scheduling option is disabled for your Activities.
If that feature is disabled, the auto-engine does not run for that Activity.
If you would like to create the Instance dates but not automatically assign volunteers then, you can disable the auto-scheduling at the Workgroup level and enable it for the Activity.
This will create the dates but no volunteers will be assigned.