That message means the same thing as the red LED on a Hub 3.
If it continues to recur after a pinhole (or software) reset, then it's either genuine overheating and needs replacing, or it is a faulty heat sensor, and still needs replacing. Genuine overheating won't normally be obvious from the outside of the hub, since the total heat generated usually isn't any greater than normal, but what's commonly the cause is poor contact between CPU die and the CPU case, or between the CPU case and the heatsink. With poor contact, the (say) 7 watts going into the CPU isn't conducted away fast enough, so the temperature build and builds, until it exceeds the limit, triggering the sensor, and the firmware then throttles the CPU and logs the error message.
Thermal throttling should keep the hub working, but it will impact performance. If your use is casual enough then you may not notice, but it would be more apparent either for higher speeds, or larger numbers of connected devices, or for latency-sensitive uses. Personally I'd not accept any excuses, I'd want an overheating hub replaced, and I'd make sure it was, but bear in mind that it may not be replaced with another Hub 5.
If anybody tries to tell you that this is normal, or that it's OK because the throttling has kicked in, then that would show that they didn't have a clue about the matter.