I've often been unable to connect to SSH on a host for lack of available CPU/memory to spawn the SSH receiver process + the shell.

It's especially a problem with AWS's tN.micro instances: when something thrashes them for long enough, they ratchet down to such a low CPU allocation that it will likely take hours before SSHD gets context-switched to enough times to start your process. By then, all sorts of timeouts will likely have killed your session.

That's worth making persistent noise about, I think. Because you just described something that can be accurately described as a type of DoS.

Considering the number of AWS credentials out there, I can see malicious users logging in, forkbombing the instance, getting it to throttle back, and then walking away whistling until the person with dashboard login wakes up and can reboot the machine.