For sure, there was no doubt it's a Hikvision server, but the NVR is communicating literally every single second. It wasn't doing that on earlier firmwares and it's not doing it on the very latest, so I conclude that it wasn't correct.
I tried downgrading to the previous V4 release but this was still happening. I've now upgraded to V4.30.055 build 201111 from the European site and this is fixed.
Has anyone else noticed their NVR trying to interact with devlog.ys7.com the those time? What's this about? I've blocked these queries on my Pi-hole for now.