I had the exact same issue:
GlassWire adds it’s own entries to the Windows Firewall for each app you have allowed/blocked. These appear as numbered rules; e.g. Glasswire.app.in_123
It would seem that this configuration can become corrupted which stops the firewall behaving as expected. The solution I was given was the same as you did; nuke all settings and start over. This is less than satisfactory if you have a lot of rules and other configuration settings to recreate.
There is a horribly manual method of backing up and restoring your GlassWire database, but I doubt this will help with the firewall. This could certainly benefit from some improvement: