Problem with periodic automatically generated mailing list. Why is there multiple release generation?

Question

1C-Bitrix

Colleagues, hello..
I encountered a problem while creating an automatically generated mailing list (the latest version of Bitrix). Checking the need for mailing in the module settings (via the Bitrix agent) is set by default (60 seconds). In the mailing itself, I set automatic generation every 1st and 15th day of the month at 8:00, left the days of the week empty, put the last mailing on the 1st day. The mailing component itself has changed somewhat - the filter that selects items for mailing has been configured in such a way that all elements with an additional date property between today + 14 days and today + 28 days (newsletter about future events) get there. As soon as I check the box "Active" and save (and it was on the 14th), then every minute the issue starts to be generated and sent to everyone (to 3500 addresses ..).
Colleagues, what am I doing wrong? What is the mechanism for checking the need for mailings in Bitrix?
Who has experience in creating automatic mailings (news or upcoming events)..