Best answer by Elias_P
Do the following checks:
- open the Lab in incognito mode,
- press the "StartLab" green button on the left up corner. Does it shows that it is ready to use or is it uploading the Lab's resources? If it is uploading, then you'll have to wait. Don't try to Log In before the upload of the Lab's resources finish,
- In case that still nothing changes and you still have the same problem then just send a message to the Support of the Qwiklabs. They usualli answer very fast, no ore than a day!