The main error that I posted about is from google chrome. firefox also throws and error but it says:

Corrupted Content Error
The page you are trying to view cannot be shown because an error in the data transmission was detected.The page you are trying to view cannot be shown because an error in the data transmission was detected.Please contact the website owners to inform them of this problem.

I just attempted to use the new microsoft edge browser on one of my win 10 machines and it gave no error and downloaded perfectly. No issues. I'd try internet explorer, but I have that garbage disabled.

I do have those files in /root as well as /home/user.

I found the newly created folder in /root/themes. Even though ubooquity is installed to /opt/ubooquity. I followed the exact same tutorial that James did in case it helps. I added the themes I downloaded to /root/themes and all is well. They worked perfectly.

I'm actually having the same problem on a headless ubuntu server. I have placed two different themes in /opt/ubooquity/themes as well as the theme folder in the home directory. I have restarted the server multiple times. I also tried to create a new theme from the admin panel which shows up in the theme selector, but I cannot find the folder it created in either directory. This one has stumped me.