After I downloaded and installed LibreOffice 6 (using torrents), I found that when I attempted to restart Windows 10, it seemed to go into an infinite loop–either that, or it just hung up. All I saw on the screen were those rotating dots, and nothing else! I finally had to use a backup copy of Windows to perform a System Restore, which returned me to LibreOffice 5.4. This suggests to me (and I’m NOT an expert on Windows by any means!) that something may be wrong with the Windows installer for LibreOffice 6. At the very least, I would respectfully suggest that you begin your trouble-shooting there.
You may try to troubleshooting it by running Libreoffice with --safe-mode from the command line.
Example (type the following in the command line):
"C:\Program Files\Libreoffice\program\soffice" --safe-mode
In my case, I disabled OpenGL and it worked.