Realising that 50/10 unlimited is sufficient for our needs, I downgraded our 2D package from 312/108 earlier this week. However, since the transfer, we have been plagued by intermittent connection failures between the supplied Orbi router and the fibre connection. The Oribi reports a connection problem and I reboot the Orbi and then all is well until it loses its connection again.

2D support ran me through a factory reset of the Orbi router but the problem persists.

If I didn't know any better, I'd say that 2D intentionally degrades their own cheaper network and makes it unusable so that you don't downgrade ;) 

The issue appears to be exactly as described here:

https://www.geekzone.co.nz/forums.asp?forumid=81&topicid=306304

I've sent 2D another support request. Any suggestions on how to proceed from here. I'm getting itchy fingers to can 2D and move to a different ISP - but it really may be a technical fault that needs correcting.