Enermax has had a lot of issues in the past with their AIOs. A 240mm one should be enough to keep the 10700K cool, but odds are the AIO has just failed. They tend to get gummed up and while they still pump liquid around, it doesn't do much to help keep the chip cooled.
I'd RMA it, though odds are they'll just ship you another one that'll fail.
As for whether or not you've damaged it, the shutdowns are designed to be protection to make sure the CPU doesn't get damaged. You don't exactly want to be doing it, but it should be fine.