I actually came on here to ask "Is there a way to reset links down" until I read that rebooting the router resets this counter! So that's now led me to ask why so many links down?? The hAP ax2 had only been up two days and pretty light use. 14 devices connected at the moment, most of them on 2.4GHz channel.
I've rebooted it again and will keep an eye on it.
What actually constitutes a link down event? I know that making a configuration change anywhere in the interface configuration tends to cause the link to go down and up - that's understandable.