Calendar event is replacing existing attachments when updated with new attachments using my add-on app

Question

My add-on app is integrated into Google Workspace and is used to select files as attachments from app.

In a calendar event when attachment icon is clicked, I can see my app which will allow to list files to be selected. On save, Event gets saved but when the event is reopened to add additional attachments using the app, I can see the files being added to the event attachments before save action. However, after saving the event, the old attachments disappear and shows only the recently added attachments when I reopen the event.

I could not see any errors in the console/network tabs of Dev tools either.

Each time when I add a file, below payload is sent to workspace api:

{ "renderActions": { "hostAppAction": { "calendarAction": { "addAttachmentsActionMarkup": { "addonAttachments": [ { "resourceUrl": "/design/DAGNmGUDFgY/edit", "title": "Private", "mimeType": "application/custom", "iconUrl": "/favicon-1.ico" } ] } } } } }

The only exception seems to be files from google drive which works fine.

Any assistance would be appreciated.

On save action, I would expect the event to retain the previously attached files as well.