Bulk Emails are not sending from LearnDash Course Reports page

Hi,

I use LearnDash plugin to host online courses on my site. Under the LearnDash LMS < Course Reports tab in the WP Dashboard, we (admins) can track students’ course progression reports and send bulk or individual emails as necessary.

After installing SparkPost (I am a premium user), I am not being able to send bulk email notification to all my students. After clicking ‘send’, the browser keeps loading for a long time and then shows a 524 error. However, I can still send email from this panel to individual student.

Before installing SparkPost I was using default wordpress mail functionalities. But I faced issues in email deliverability and installed SparkPost SMTP. All of my other transactional emails are still being delivered with sparkpost, just not the ones I send (in bulk) from COURSE Reports panel.

I contacted LearnDash and they said:

as you have referenced, by default email deliverability is handled by WordPress and not LearnDash. Now, on the other hand, as the issue started happening after installing the SparkPost third-party plugin, it seems that this plugin is causing a conflict with the Notifications add-on. This issue is out of LearnDash control. I suggest you to get in touch with the plugin’s support service about this issue.

Note: I tried both SMTP and HTTP method.

The page I need help with: [log in to see the link]