As summary, on macosx 10.10.5 on first run LibreOffice stuck on "Verifying" and does not proceed.
Tried on High Sierra and had no problem.
Steps to Reproduce:
1.Open LibreOffice dmg installation
2.Copy on Any folder (even application folder)
3.Double click on it
The "Verying" window opens and the progress bar runs fast to the end but then it remains stuck.
User Profile Reset: Yes
OpenGL enabled: Yes
*** This bug has been marked as a duplicate of bug 89657 ***
@Simone : try executing the following command from a terminal before attempting to start the LibreOffice.app:
"xattr -d com.apple.quarantine /Applications/LibreOffice.app/"