Ok, so this is really frustrating - other people seem to be having this issue too.
I'm getting the site lockout emails while I'm working on my site, these one's "too many attempts to access a file that does not exist"
This is not the sort of thing I expect to have to deal with when I upgrade, it's certainly fast putting me off this plugin.
Thankfully this is only happening (to me) on my own site right now, but if this started happening on client site's - that would be a nightmare.
I'm going to try whitelisting my IP to see if that has any positive impact.
If anyone has any bright ideas - please let me know.
I'll post back any success I many have.