@Gertjan and others:
It was very helpful to understand that pfsense has a lockout which I had not seen before. What complicated issues further was that every now and again the connection between my browser and the pfsense firewall would go down momentarily. I traced that to an Ethernet NIC - after testing it with other machines. I would just watch the ping between 2 workstations connected directly by ethernet with no intervening switches or routers and every 2-20 minutes, the ping would not be returned for maybe 20 seconds. I am sure that this did not help. Exactly what effect it would have, I'm not sure - maybe receiving a spurious version of my pw etc. But I admit that I don't really know. So perhaps this was a combination of being locked out, problems with the NIC and general incompetence on my part ;)
As far as I can tell, there are no remaining login problems. So thanks to all who responded.