Notifications are only sent out to users if they've been assigned under the 'Status' column within the checklist they're working on. Without this, you won’t get notifications when a user uploads new documents, leave comments, or make changes to the checklist.

Please be aware, that if you tag yourself in any line items in the checklist, you won't receive notifications either.

You also need to check whether notifications are enabled on a matter level and a user level. To check this please visit this support article for further information.