Meeting notification sent periodically and without reason

Hi all,

Recently in my organization every Monday more or less at 2:40, are sent meeting notifications with "No response required" from a set of users to the attendees of each one of meetings. 

I saw in explorer that each one of messages are generated from exchange online servers, from multiple IPs and some of them with IP 0.0.0.0 associated. 

I would like understand what could be causing this behavior, since users are not the ones triggering these notifications and we don't have any schedule configured. All notifications generated go with "no response required" and some of them go directly to deleted items of recipients and others to inbox.

Anyone else with this behavior. I saw the meeting options in some outlooks and nothing explains this behavior.

Thanks!