Reminders will not Upgrade - Solution FYI

My Reminders would not upgrade across multiple devices. After a LOT of frustration, I finally got it, I am sharing my solution.

I had thousands of completed/deleted Reminders. First, I turned off iCloud sync on all my devices, leaving the reminders on the web iCloud hosting site only (risky!). Next, I had to go use the iCloud web interface and clear these. Sounds easy, right? NOPE. The iCloud web page would show zero completed tasks after clearing, but a reload would have them right back, only slightly fewer. Apparently, clearing old completed reminders requires a supercomputer, or Apple is hosting these for the world on a single old Mac! It took all day, processing, freezing, reloading the page, just to find out only a relatively small number more of them had been deleted. I would sometimes get a LOCKED FOR MAINTENANCE message, or it would just be frozen, partially whited out. After an unreasonable amount of tenaciousness, led on by the slowly decreasing number of completed tasks remaining to be cleared out, reloading the webpage, waiting as it processed, reloading..., I got all the completed tasks cleared out. And behold! The web version upgraded! I was then able to turn iCloud sync back on on my devices and they too upgraded.

Frankly, this was crazy, but it did finally work. Very disappointing, these are essentially text files. What's up Apple? This should happen in the blink of an eye!