Problem in Communication mails while using membership plugin

We are using Communication section to send emails in regular interval

to users. Emails are not sending on right time. We are getting

shuffles emails in different interval, please help on same.

Here are dates below of the email we have received so far as the user

ask@thehappypear.ie

Signed up on the 10th and received 1st email.

13th reveived the 2nd email (the day 3 email)

17th received the 3rd email (the well done for making it thro week 1

mail)

19th received the 4th email (the exercise one)

– should have received the 5th email on the 21st (11 days after

signing up) but it never came

– should have received the 6th email on the 24th (14 days after

signing up) but it never came

on the 28th (today) should have received the 7th mail but instead

received the very first one thanking me for signing up.

– today at 12.43 we received the “day 3 update which is the second

email)

Please help on same as it is main part of our website.