Not all emails are coming to firewall.

I am using google app domain. Problem is that all mails are not delivering. If I send 10 mails, two or three are not delivering. Checked at firewall end. If any mail is coming to firewall, that get delivered. No issue with firewall side. error message is

The response was:
The recipient server did not accept our requests to connect. Learn more at https://support.google.com/mail/answer/7720  generic::failed_precondition: connect error (0): error]


There was a temporary problem delivering your message to abc@xyz.com. Gmail will retry for 22 more hours. You'll be notified if the delivery fails permanently.

Last-Attempt-Date: Mon, 11 Dec 2017 17:16:30 -0800 (PST)
Will-Retry-Until: Tue, 12 Dec 2017 15:42:11 -0800 (PST)

Mails from all other domain are delivering. Only with one domain(google domain) has this problem.
Please help.
The domain mx are
      aspmx.l.google.com
      alt1.aspmx.l.google.com
alt2.aspmx.l.google.com
      aspmx2.googlemail.com
aspmx3.googlemail.com
aspmx4.googlemail.com
aspmx5.googlemail.com
We checked all end and guessing problem is google side.

Thanks for considering my request.