EBS R12 Workflow notification mailer not sending emails although Workflow Mailer Service is activate

Hello all,

Our system have already using Workflow Notification Mailer service.

But Sometimes it sends only Notifications To users Without any mails although when we navigate to responsibility  workflow Administrator web application >> oracle application manager  >> workflow manager >> service component >> Workflow Notification Mailer >> Workflow Mailer Service

we will find that (Workflow Mailer Service )is activated as in screenshot, so i have to restart all To resend mails again every time .

So what should i do to solve this problem please .