I think I've fixed the problem. I had manually entered my WiFi hub in ZoneAlarm as a "subnet". Here's how I fixed:
Disabled my WiFi connection.Seems to be working since then. If it fails again, I'll post a follow-up entry.
Removed all references to my WiFi from the ZoneAlarm Zones.
Rebooted, reestablished WiFi connection.
Turned on ZoneAlarm. It detected the WiFi connection and automatically made a Trusted Zone Entry of type "Network" (an Entry Type which is not available for manual setup).