Does anyone know what this is? I've set up a new classroom and have several students, plus this: tu.8zPhLpMrvaLOi tu.8zPhLpMrvaLOi@duolingo.com I tried the email and it's invalid.
A glitch happened while they were connecting to your class. Use process of elimination to figure out which student, then have him log into his account. (If he can't get in, it's because he is new and didn't finalize something somewhere, and he will have to make a new account. But that's not terrible if he is new.)
Tell him to click on the blue silhouette in the upper right.
Next, click on settings.
Next, click on progress sharing.
Now he can enter your classroom code.
You may be left with the artifact of the wacky e-mail. You can delete it.
This happens to me maybe twice a year, but this fixes it 100% of the time. Hope it helps you!