Microsoft Lists - The requested operation is part of an experimental feature that is not supported..

Oh yeah, someone in development definitely broke it and I think they're scrambling right now trying to get it fixed.  I wasted like 4 hours today trying to figure it out and I think it's a bug deep in the foundation code that got pushed out in a recent update.  I've have 2 Office 365 E5 accounts (Development and Corporate) and my dev account is about 5 years active and the corporate one that I'm the admin for is about a year.  Both accounts have used lists previously.

This morning on my dev account I could a list to an existing sharepoint site, but if I tried to do create one and add it to My Site, it popped the error.   On the corporate account I couldn't add one to a SharePoint site, or My Site.  Here's where things get a little weird.   Currently, at the time of writing this I can now create a list from a template to both of my accounts in both SharePoint and My Sites.  But......  only in my dev account to a SharePoint site can I create a new list that actually is the modern theme.  When I create one and publish it to My Sites, or a SharePoint site on my corporate account the newly created list comes up in SharePoint 2013 format!  If I go to list settings / advanced settings / list experience and change the option from "Default experience for site", to "new experience", BAM, it's back.  Please note that I know these settings haven't been touched in my dev account in years, because the account has been sitting dormant for the past 9 months, so I know it isn't something I done.

Lastly, for a major WTF moment.  I can create a list successfully to all 4 options I've listed above on the iPad ios App and it works beautifully!  One major hitch.  When you get on a web browser and try to access the list created through iOS it's no where to be found.  I had to navigate into the Site Settings / List and Libraries to find them.  Then when I opened them through the web browser they reverted back to SharePoint 2013 style.

I don't know why I would assume that the largest software company in the world would test this crap before pushing it out.  What a mess.  I feel bad for those that are using lists in a big environment right now.