When upgrading or installing UIM 20.4, the installer sticks at 5% on the "installing uimserverpackages.zip" stage and never makes any progress. We have waited 15 minutes with no movement.
Antivirus
Issue was determined to be caused by Symantec Antivirus performing a weekly scheduled scan during installation time.
Snoozing the scan immediately allowed the installation to proceed past the 5% mark and complete successfully.