Send outlook email - email not sent and no error meesage or exception found


I have created a workflow which includes sending email notifications. It sends 1 kind of notification when a condition is true and a 2nd kind of notification when the condition is false. At times the email is not sent when the condition is true and I do not see any error message or exceptions being thrown.
There are 2 activities after the “send email” and they get executed and the workflow completes successfully. Any ideas what might be wrong? I have tried it using different email accounts on outlook on different machines. The issue just occurs randomly and it seems that the send outlook email activity is just skipped…