Noticed that MarsEdit was giving errors when trying to login to my WordPress blog. Similarly the wp-admin page would go into a login loop. This didn’t always happen. It looked like some public IPs of my ISP were being blocked. (I’ve seen similar behavior with Teams audio too. On some of my public IPs audio doesn’t work; disconnect & reconnect my WAN connection to get a new IP and if that’s from a different subnet it usually works).
This could be because you have JetPack installed on your block and it’s set to block brute force attacks. The solution is to login to the wp-admin page somehow, then go to JetPack > Settings > Brute force attack protection > expand it > and add your IP to the whitelist section. Repeat of course for each time your public IP changes. (Or you could disable JetPack’s protection I guess, I didn’t want to do that).
My guess is JetPack and whatever else that occasionally doesn’t work me is because some of my public IPs/ subnets are in some database somewhere which marks it as belonging to hackers or bad actors and these database are what is used by all these services to blacklist attacks.