Experience Cloud Users Can't See Tasks Created by Other Users on the Same Account

Hi Trailblazers,

I'm facing an issue with Experience Cloud and would appreciate your help.   

Scenario

Portal users create Tasks directly from the Experience Cloud portal. They do not have access to the Salesforce org.

They can access an Account record, but they can only see the Tasks they created themselves. They cannot see Tasks created by other users (internal users or other portal users), even though those Tasks are related to the same Account.

Current Setup

• Activity OWD = Controlled by Parent
• Portal users have access to the Account record.
• Tasks are related to the Account (WhatId = Account).
• Portal users have the required object and field permissions.

Issue

• If a portal user creates a Task for an Account from the Experience Cloud portal, they can see that Task in the portal.
• If another user creates a Task for the same Account, the portal user cannot see it in the Activities related list. They only see the Tasks they created.

Is this the expected behavior with Activity OWD = Controlled by Parent, or is there any additional sharing or configuration required to allow portal users to see all Tasks related to the Account?   

Any guidance would be greatly appreciated.   Thank you!