Hi,
Please give below work around a try and let me know your results.
You should be able to work around the issue by first Activating the sandbox (solving puzzles, reviewing/accepting permissions, etc.) and then once you see the sign-in box appear on the right open a new browser tab.
In this new tab, browse to https://portal.azure.com/learn.docs.microsoft.com and complete exercise instructions.
For other exercises that require Azure Cloud Shell, you would first Activate sandbox as described above (if one isn't already active), and then once you see the sign-in box appear on the right open a new browser tab. In this new browser tab you would browse to https://sandbox.azure.com
When prompted, click Bash (Some exercise may use both PowerShell and Bash. You can switch between them using button at top of cloud shell window)
Next choose No storage account required, for Subscription select Concierge Subscription, and click Apply.
After several seconds delay while a cloud shell is requested and connected to, you should see $ prompt. At this point you can complete the exercises instructions, copy/paste code from exercise tab to cloud shell tab as needed, etc.
Please click Accept Answer and upvote if the above was helpful.
Thanks.
-TP