Apologies you're experiencing this issue.
I tried the same steps (Unit 3>Task 1 > Step 2) , and it worked fine.
If you haven't tried this already, please try these:
•Change the --version 2.1 to --version 2.1.7 and see if it helps.
•Users were able to resolve the issue by restarting the sandbox
Also, please note that the sandbox environment created for a module is available for four consecutive hours to ensure that you can finish the module. These exercises are meant to be finished in one sitting, in an hour or less.