EWS API: Anything I call update_item for a meeting, it ends up canceling the meeting for any attendees - exchangewebservices

Question

I'm using the EWS API (targeting Exchange 2010) I cannot figure out why anything I make a request to update a calendar meeting/item. Is there something I'm missing or is this the expected behavior? I'm able to make a change from Outlook to the meeting without it sending out a cancellation email to all attendees except the organizer.
The below is a sample of the relevant portion of the SOAP request. I replaced the actual attendee's email addresses, item ID and change key.
{:send_meeting_invitations_or_cancellations=>"SendOnlyToChanged",:conflict_resolution=>"AutoResolve", :item_changes=>[{:updates=>[{:set_item_field=>{:field_uRI=>{:field_uRI=>"item:Subject"},
:calendar_item=>{:sub_elements=>[{:subject=>{:text=>"Thursday 11AM Recurring"}}]}}},
{:set_item_field=>{:field_uRI=>{:field_uRI=>"item:Body"}, :calendar_item=>{:sub_elements=>[{:body=>{"BodyType"=>"HTML", :text=>"HI"}}]}}},
{:set_item_field=>{:field_uRI=>{:field_uRI=>"calendar:Location"},:calendar_item=>{:sub_elements=>[{:location=>{:text=>"LA, CA"}}]}}},
{:set_item_field=>{:field_uRI=>{:field_uRI=>"calendar:Start"}, :calendar_item=>{:sub_elements=>[{:start=>{:text=>"2019-03-07T19:00:00.0000000"}}]}}},
{:set_item_field=>{:field_uRI=>{:field_uRI=>"calendar:StartTimeZone"}, :calendar_item=>{:sub_elements=>[{:start_time_zone=>{"Id"=>"UTC"}}]}}},
{:set_item_field=>{:field_uRI=>{:field_uRI=>"calendar:End"}, :calendar_item=>{:sub_elements=>[{:end=>{:text=>"2019-03-07T19:30:00.0000000"}}]}}},
{:set_item_field=>{:field_uRI=>{:field_uRI=>"calendar:EndTimeZone"},:calendar_item=>{:sub_elements=>[{:end_time_zone=>{"Id"=>"UTC"}}]}}},
{:set_item_field=>{:field_uRI=>{:field_uRI=>"calendar:RequiredAttendees"},:calendar_item=>{:sub_elements=>[{:required_attendees=>{:sub_elements=>[
{:mailbox=>{:name=>"Joe ABC",:email_address=>"joe#abc.com", :routing_Type=>"SMTP"}},
{:mailbox=>{:name=>"John ABC", :email_address=>"john#abc.com",:routing_Type=>"SMTP"}}]}}]}}}],
:item_id=>{:id=>"AAMkAGJjNWIzNzI2LTM1N2YtNDVkMi05NzU5LTRj",
:change_key=>"DwAAABYAAADWK9s0Y5iSSLP"}}]}

Answer 1

If you use Set_Item_Field to update the required attendees this will overwrite the current property so if any attendees aren't in the updated collection your effectively canceling the meeting for those attendees. If you want to use Set_Item_Field to update attendees then you need to include all the attendees for that type because your replacing the collection for the recipient type not appending to it.