Make sure you’re using the latest version. It’s always available in ParagonBox.
Make sure the driver is enabled: Open the application interface, then use the menu bar to navigate to Paragon ExtFS for Mac 11 – Preferences… – General. Paragon ExtFS for Mac 11 should be “Enabled”.
Make sure the program is activated, or trial period hasn’t expired.
If the problem appeared after updating the previous version, please try uninstalling the software using downloaded .dmg file, reboot your Mac. Reboot your Mac again after installation.
If the problem appeared after OS X update, please reinstall the driver.
If the disk is not mounting, it makes sense to perform a file system check (On Linux systems: fsck -f for ExtFS disks) before further troubleshooting.
ExtFS for Mac does support Ext4 partitions formatted with 64bit option.