Thanks for the quick and detailed reply.
Something I did when I followed your outlined steps got things working. Unfortunately I don’t know exactly what it was. Nothing I did before deleting and reinstalling the plugin worked. After reinstalling the plugin I immediately checked the status of the log and it was still showing as missing so I hit the delete button and it created a new log. But it did not show the log as having been deleted because there was no log to delete. When I pressed the button a second time I got the delete message. It was only after doing all the above that I again tried to register with a known bad email and it was denied.
Some more details, in case they help:
My site is using bbpress, but my login spam is all coming from the standard login page which has not been modified. There are no public pages with open comment forms.
I tried deleting the log and it successfully created a new log. I did not get the deleted message because there was no old log to delete. When I deleted the newly created log I then got the deleted message.
Force resetting the options did not fix the problem.
My best guess is that reinstalling the plugin solved the problem. I should have done that before posting. It doesn’t seem likely, but I suppose it is possible there was something with creating the log file that solved the problem.
Now I will go change the options to what I had.
Thanks again for your help.