Cannot share a classic SharePoint calendar with External Users

We found a bug almost two years ago (Sept. 2015) in SharePoint Online when trying to share a calendar with an external user.  Our business user wanted to grant access only to the calendar in their SharePoint site to the external users, so we came up with this (admittedly crazy) workaround:

We created a subsite to the site with the calendar, with nothing in it. We then instructed the business users to:

1) Invite the external person to the subsite

2) Confirm that they are able to log in

3) Grant them access to the calendar

It seemed to be related to the initial sharing invitation for new external users, but I'm a little fuzzy on those details.

I did find the email thread with Microsoft support (ticket #115092213185735 ), but the KB article they referenced is no longer available:

Issue: You were seeing invitations to a calendar item fail to send when inviting users for the first time. 

Resolution: I explained this has been known to occur for new users when permissions in lists items are unique https://urldefense.proofpoint.com/v2/url?u=https-3A__support.microsoft.com_en-2Dus_kb_2938827&d=AwMFAg&c=5MrMVID9Pd61bTJfp9wNBTxRZN_CiHJui8q3SJEDr28&r=rH_5r9pqFASPwvQ9kq1liWACr8zlp6n51XJP9I6B6Z7qBlsKWel3cAuOanDPJLfw&m=qSYbt8nZac_fIx_QYvRiTYeZ5j0266li0ydewlsXxmo&s=4QnYqVsKv9JWMU9B_8R_cCkEJblGAvxBTx_AmJWxSlE&e=. Though the users can be invited to the entire list/calendar without issue.