Activities can be marked as completed through opportunities social pane regardless of fulfillment of business required fields, causing compliance failures and breaking all workflows that are dependent on required info input.

During the customer sales process, as the user advances to the next phase, some tasks are automatically created and the user shall complete then and fill all required info on it.
The issue is that although the task have some business required fields and the tasks cannot be concluded (Marked Complete) on the task form without adding all required fields, as expected, if the user go, instead, to the opportunity�s social pane and click �Complete� on the task, the system will mark it completed ignoring the business required fields requirements, causing a compliance issue, allowing a not executed task to be completed and breaking all workflows that depend on this information not filled.

Note: issue happens when no out-of-box fields are marked as business required fields on main form, such as Category field.

Workaround
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Remove the conversation tab (Social Pane) from the opportunity form.
However, the customer is not happy with it.
Removing the social pane also removes the notes and posts panel.