We have problem on Exchange 2013, response of attendee for other attendees is not retrieved from Exchange server, via EWS and also in OWA. In Office 365 it works.
Of course - all replies only go to the organizer, the attendees never see the updated responses.
It is a recent Office 365 feature that allows the attendees to see the responses as well. See https://support.microsoft.com/en-us/office/attendees-can-see-others-responses-to-a-meeting-invitation-f51437e5-352c-4223-b7d8-7020cd71f3c8