"After releasing updates for all FabFilter plug-ins on February 15, we have discovered a bug in the FabFilter Pro-G expander plug-in that could cause it crash or work incorrectly on mono tracks. This bug has been fixed in version 1.20, which is now available for download for Windows and macOS.
Of course, this update is fully backwards compatible and free for existing Pro-G users. We recommend all FabFilter Pro-G users to update to version 1.20 as soon as possible.
To update your existing FabFilter Pro-G plug-in, just download the new FabFilter Pro-G installer and run it. No need to uninstall first or enter your license key again.
Download the update now: www.fabfilter.com/download
System requirements on Windows are either Windows 10, 8, 7, Vista or XP and a VST 2/3 host or Pro Tools, or Mac OS X 10.6.8 or higher with Intel processor, and an Audio Units host, VST 2/3 host, or Pro Tools. Both 32-bit and 64-bit hosts are supported." -Fabfilter.com