Something similar happened to a family member some years ago.
All the maps were digitised and so in some cases differences arose between the reality on the ground and the new digital map. Unfortunately the map has to be 'rectified' before a buyer can purchase.
In the case I am aware of the owner was known, until it was discovered that the registered owners were in fact his deceased parents. The deed of rectification had to be agreed by all his siblings, including one who lived in Australia.
What finally prompted them all to agree was that part of their property was in 'our' site. Had they wanted to sell they would have faced the same issue.
It might be worth enquiring if this is the case here, I think it is a common difference in the digitised maps, where a boundary at an angle to a road is mapped as perpendicular.