g.fast master socket / ppp / regrade issue with zen

I got g.fast internet installed from zen internet, unlimited fibre 3 as that is all I could order due to the checker saying g.fast was amber availability. When the engineer installed it, I had just moved to the property, and could not find a master socket - he said it was fine installed a g.fast box into the wiring of one of the existing sockets. I have since found a master socket in a cupboard...

Despite not using the master socket, the install was working fine, with max g.fast sync speeds of around 150/30 as expected, so I asked for a regrade to ultrafast 4. This got stuck on zens order systems, but was put through yesterday (11/12). Since the regrade, I can see my sync speed is showing as downstream 291378 - 301024 and upstream 42582 from zens portal, but I am unable to make a PPPoE connection, either from the router or with an osx laptop, either using my zen username and password or the bt test logins. Both giving me a Chaps authentication error. Zen have said this is an openreach fault, and logged an engineer visit tomorrow.

I guess I have 2 questions

1 - could the fact the g.fast has not been connected to the master socket have any impact on this? Should I mention this to the engineer, or am I likely to get charged for it as it is an issue with my extension wiring (even though the original engineer installed into the extension wiring...). Is the engineer tomorrow likely to reinstall at the master socket? I would actually prefer this...

2 - More for interest, but why is a PPPoE authentication issue likely to be an openreach fault? From some reading, does this mean i'm connected to the BRAS wrongy? Are there other reasons this can happen? Can line quality affect this?

The fact your syncing at the speeds you are suggests the wiring is not having a significant impact - the engineer may even have done something to cut out some of the wiring. If an engineer is coming to the house then worth mentioning the install as it is possible that the original didn't do it the right way.

No matter what though the CHAPS error is not the wiring. It is in the Openreach network. I am not certain if it is BT or Zen that provide the CHAPS authentication - either way though I would have thought it would be a software fix rather than needing an engineer to attend. You may get no engineer actually turn up to the house as the fix may just be done remotely.