I have a pretty peculiar problem with the sandbox exercised on the Learn site. Doing the tasks perfectly and afterwards pressing the 'Check your work' button almost always results in a 'That's not quite right' message, even though the sandbox is perfect.
I know this because after pressing the button numerous times, logging out, logging in, trying a different browser, eventually makes it produce the 'Great work!' result. Sometimes it immediately has that result, sometimes it takes many, many clicks. No idea what I can do to help that.
The only reason I can come up with is that my email is connected to two different accounts (it seems) as it asks me to say 'work' or 'private' whenever I login using my Microsoft Account. I always use my private account but the work one somehow also has stuff set on it. For the record, it is not my work at all. That uses a completely different mail adress with a different domain.
Both appear to have Azure domains as well (although I only use the private one). I've looked around to see if I can fix this myself, but the help I find Googling is cryptic and doesn't really help at all -- I don't own that domain it thinks I do, so I can't provide TXT domain settings to remove anything at all. It's more than a little disheartening to see how utterly convoluted the Microsoft account system is now.