Every time I log into the Launcher and try to play the Demo, it says that it couldn't download some game files without internet.

This happened basically today.

So, I was on the Launcher after I logged into my account. I just downloaded the standard one and just tried to play the demo version of Minecraft. My internet is actually fine, but every time when I try to play one of the versions, it says: 'Some game files are missing, and can’t be downloaded while the launcher is in offline mode. Please connect to the internet and try again.
Name: Game files are missing'
I am so confused. I looked at my internet, noticing how it is still good by being at 4 bars. It kept saying that I had no internet to download the rest of the game files. Why is it causing this issue? Was it because I accidentally closed the Launcher when it was downloading files or?