Full resync of iCloud drive data without reason

Today one of my iMacs decided to resync (upload) the entire contents of iCloud drive (90+ GB) without any reasonable justification. I have several macs linked to the same iCloud account and the only action that might have triggered this behavior is that last night I unlinked one of my macs. That, however, should have only affected the local storage on that mac.

I should say that I've run in a similar issue more than a year ago with 10.11.x Sierra and a different iMac. On that occasion I submitted a bug report and through the course of several weeks escalated up to the iCloud developers, but nothing came out of that. The problem solved itself after a full painful resync.

This is really not a question, just a post out of frustration. I doubt that an easy fix can be implemented: I'll have to go through the whole process again... I wonder how someone with 2 TB of iCloud data might feel when something like this hits!?