Sadly, updating robots.txt didn't solve the problem.
1 registered members (1 invisible), 1,780 guests, and 10 spiders.
When I spot-check the IPs of the "guests" "logging in" they are mostly from overseas:
We had the same problem The last time it happened, our website was down for three days. That's when we threw up our hands and implemented Cloudflare. That's the best decision we've ever made.
Look at this. Half our traffic was blocked by Cloudflare. (The half we don't want.) It's been as high as 70%. Cloudflare (for us) is free.