C5 owner here - I am impacted by this issue, My ISP is not blocking access to pool.ntp.org servers (verified via tracert and ping).
Ever since I shutdown/unplugged my hub and rebooted it, my C5 has been going crazy trying to hit #.pool.ntp.org ever 1-2 seconds. Here's what I see via my Pi. The slight dip was when I had my hub unplugged for 5 minutes.
Here's an example of what I see in my logs via my Pi:
I've tried changing my DNS from Cloudflare, to OpenDNS, to Google (8.8.8.8) and nothing seems to enable the C5 Hub to feel satisfied and stop it from continually trying to access #.pool.ntp.org. I can reproduce the issue where my hub tells me to register and my clock on the hub becomming incorrect by simply going to settings > shutdown then unplugging and plugging the hub back in.
