Thanks for using Soft U2F. I'm sorry that you've encountered a bug.
To aide in debugging, please provide the output from running the following commands:
FIDO U2F only works natively using Chrome and Opera. Browser extensions enabling U2F are available for Safari and Firefox.
This tells us the version of macOS you are running. Soft U2F only works on macOS Sierra (10.12) and newer.
file /Library/Extensions/softu2f.kext /Applications/SoftU2F.app ~/Library/LaunchAgents/com.github.SoftU2F.plist
This confirms that the various components of Soft U2F were successfully installed.
This confirms that the Soft U2F driver is loaded.
This confirms that the Soft U2F app is running.
This grabs logs from your installation of Soft U2F. Other system details are included in this log file and the command attempts to filter the file down to details that might be relevant to Soft U2F. Still, you might want to verify that no information is included in these results that you aren't comfortable sharing.