Netgear Orbi RBK40: Purple Light / dropping WAN connection

My Netgear Orbi is plugged directly into my ISP's fibre router, and multiple times per day the Orbi's purple light comes on and drops its connection to the WAN. I can't find any information about why this is happening, my ISP can't tell me. I bought the Orbi in May 2017 so it's getting old, is it just failing?

Thanks

Ben