Its just getting to hot when under load. Normal.
I have a USB desk fan blowing over my units and it runs perfectly without pausing.
One OPUS has a broken fan from a leaking cell and the USB fan still provides enough cooling.
I've never had an Opus do that even though I've red numerous reports of other people having that issue. Make sure they're spaced apart enough for proper cooling. Check the rear fans are spinning correctly and are not blocked.