504 error when mass mailing

When mass mailing via BSG World Viber, we noticed that it constantly gives a 504 error Filtered like this, there are 6k contacts https://rozpakui.crm-onebox.com/admin/shop/users/mailing/bsgworld/?filterphone=&filterclientid%5B%5D=&workflowinid%5B%5D=12&filterincdatefrom=&filterincdateto=&filterordercountcdatefrom=&filterordercountcdateto=&countordersfrom=&countordersto=&notordertype =&filternotincdatefrom=&filternotincdateto=&filtereventindatefrom=&filtereventindateto=&filtereventin=&filtereventdatefrom=&filtereventdateto=&filtercdateorderfrom=&filtercdateorderto=&filtercustomUrovenklienta=&groupid=0&filtertypesex=&filtermanagerid=&filterpost=&filtersourceid=50&filtercdate=to=&filtercdatefrom= Making a newsletter - getting a 504 error [file]9923[/file] We don't see this kind of error in normal mailing. Server parameters have already been registered several times, does not help