Q: My new airport extreme wifi is very unstable

The WIFI of my Airport extreme 802.11ac is extremely unstable. Often the connection falls away for a few seconds and the speed varies from 80 Mbps to below 10. The router stands on a little platform on a wall and is connected to a modem with a very stable internet connection with 90 Mbps.

Is it possible that the Airport needs repair?

Thanks,

Henk