Is there any reason the lab will not finalise after stating 100% complete
Some labs will periodically take longer than the original estimate that the progress bar is based off of. This depends on a number of factors, including VM size and AWS load times. If the progress bar reaches 100% and the lab is still loading, I would check the Machines tab to see which specific systems are still loading what their statuses are.
If your lab reaches 100% and still has not loaded several minutes later, I would recommend trying the Reset Lab button at the bottom of the Machines tab.