Not possible to subscribe to meetings of certain teams with Google Calendar

[psrpinto]

The Upcoming WordPress Meetings page allows subscribing to the meetings of individual teams using Google Calendar.

However, for certain teams, Google Calendar erroneously states that the user does not have permission to subscribe to the calendar:

Steps to reproduce:

1. Go to https://make.wordpress.org/meetings
2. Select Core under "Filter by team"
3. Click on the "+ Google Calendar" button
4. Click "Add" in the popup that appears
5. The "Request access" popup is displayed

This issue affects the following teams:

• All teams
• Core
• Meta

For other teams, subscribing with Google Calendar works as intended.

(This ticket was original created on Trac)

[psrpinto]

I downloaded the meetings-core.ics file and put it on Dropbox. I then imported the Dropbox public link into Google Calendar:

(not an actual Dropbox link)
https://www.google.com/calendar/render?cid=webcal://www.dropbox.com/link-to-my-file.ics?dl=1

This worked correctly, which proves (?) the issue is not related to the content of the files, since the Dropbox file should be exactly the same as the file Google Calendar retrieves through the "+ Google Calendar" button:

https://www.google.com/calendar/render?cid=webcal://make.wordpress.org/meetings-core.ics

Maybe HTTP Response headers are the culprit. Will continue researching.