This is not an uncommon problem. Here is what has happened to a couple who are close friends of ours, prominent members of the coastal community.
They have lived in their house 20+ years. Fence lines had not changed. Mature plants lining their side of the fence on all sides.
Neighbor on one side moved out, new older professional couple moved in. New couple decided to expand their new house, did a lot line survey, low and behold the fence was 5-10 feet (can’t remember) off – our friends had part of their lot.
Words were exchanged, then letters, then both sides lawyered up. New correct fence was erected. Mature plants were ripped out. They are in a dust-settling mode right now after which I am sure construction will begin.