Guy from Openreach been and gone and confirmed the line is fine, he spent 20-30 mins testing it and found no issues,
"very good line", also remarked on the external covers and capping which I harassed Openreach for after first install.
He agree's that the line issues seemed to be the enabling of G.INP confusing the modem but said he wasn't aware of what was going on with G.INP as many will agree "they seem to be keeping quiet on the rollout dates"
So until next time (fingers crossed their isn't one) I'm happy with my connection.
Plusnet Unlimited 21CN 4200/800 > TP-Link TD-W8968v3
Plusnet Fibre Extra 66000/20000 > HG612 (Unlocked) > Linksys LRT224