Email problem - No notification for reviewers sent (partly...)

Hey there,

we have the following interesting problem here:
If journal manager A (myself, C.W.) assigns an article to a reviewer, the notification mail to the reviewer is sent correctly.
If journal manager B (Colleague D.P.O.) does exactly the same steps, the notification mail is not sent.
Screenshot of history see below.

Yet both reviewers are correctly shown in the review tab of the submission.
Any ideas about the reason for this?
It is not helpful if one has to verify every time in the submission history whether or not a notification mail has been sent …

Thank you, cw!