Blank emails when sending from Gmail via Outlook. Why?

Question

gmail

There is Outlook 2013 Standard, a number of mailboxes are connected to it, one of them is located on gmail.com. The address has its own domain other than gmail.com. So, when sending via Outlook, empty letters periodically leave this mailbox, that is, only the address remains without the subject and body of the letter (they can be seen in outgoing messages). In the Gmail web interface, the letter is also empty. If you send exactly the same letter again (body and recipients), then it will go away normally. It does not depend on the number of recipients and attachments. From other mailboxes in the same Outlook, this problem is not observed.
Somehow very strange. Maybe someone faced similar? How to solve it?