I've got 2 neighbours who have switched to Vodafone fibre and have both come to me with similar questions. I'm the local first point of call semi-geek. :-)
They are both noticing significant buffering when watching streaming video, on connections that are getting 50-70 Mbps over WiFI when Speedtested to Vodafone Wellington servers (we are in Nelson).
The sites they are using aren't any of the big players, which might be part of the issue, but the strange thing is that one neighbour still has her old Skinny 4G modem (usually around 20 Mbps max), and when she switches to that the are no streaming issues at all.
The other neighbour tried tethering their laptop to their mobile (I don't know which provider probably Spark or Vodafone, but 4G so probably similar speeds to above) and again, no buffering at all.
Anyone know what the issue might be?