Event category empty when using /api/contacts/activity endpoint

Your software
My Mautic version is: 3.3
My PHP version is: 7.4
My Database type and version is: MySql 5.6

Your problem
My problem is:
Using the API endpoint /api/contacts/activity events are returned, but any form submission events do not load the associated category. The category is set on the form but the api response shows the category property as an empty object example:

    "event": "form.submitted",
    "eventId": "form.submitted338690",
    "eventLabel": {
        "label": "[FORM ACTION NAME]",
        "href": "[URL TO FORM]/s/forms/view/993"
    "eventType": "Form submitted",
    "timestamp": "2022-03-22T12:50:25+00:00",
    "contactId": "[CONTACT_ID]",
    "details": {
        "submission": {
            "id": 338690,
            "ipAddress": {
                "ipAddress": ""
            "form": {
                "id": 993,
                "name": " submission action",
                "alias": "_submi",
                "category": {} <<<< this is empty?
            "dateSubmitted": "2022-03-22T12:50:25+00:00",
            "referer": "http://localhost:8000/index.php/s/forms/preview/993",
            "results": {
                "form_id": "993",
                "first_name": "test",
                "last_name": "test",
                "work_email_address": "test@test.com",
                "company_name": "test"
        "form": {
            "id": 993,
            "name": " submission action",
            "alias": "_submi",
            "category": {}
        "page": {}

These errors are showing in the log:

Steps I have tried to fix the problem:
Debugging - tried making category a public variable within the app/bundles/FormBundle/Entity/Form.php class to see if that returned the category but it did not.

Hmm. strange I checked it on one of my servers and strangely it really does not show the category object. Do you mind creating an issue on GitHub, thanks.

Issue created on github: Event Category empty when using /api/contacts/activity endpoint · Issue #11231 · mautic/mautic · GitHub