Lately, every time I scan system with Spybot, when I click "fix selected", Spybot does not respond and freezes. How do I stop this?

Assuming that your are running Windows 10, you may want to boot into Safe Mode then try to run the scan again. Safe Mode will shut down all unrequired programs and processes which can include malware. Below is the link from Microsoft Support with instructions to boot into Safe Mode (use Safe Mode with Networking).

https://support.microsoft.com/en-us/windows/start-...

It might be wanting resources that is assigned to other process. Try closing all unnecessary  background applications then scan it. Delete unwanted junks will reduce scan time.