Sorry for my question in english, but my french is non-existant

I have this mower for 4 years and last 2 years it has started to go left and right when following the wire. Anyone know the possible reason and solution for this problem?
The working area is the maximun(7000m2+) and the wire lenght is about 1,5km, but the bases station gives no errors and the robot dose not lose the signal, thats why i think that the wire length is not the problem.
Attached is a video of the roboto going home
https://youtu.be/WPJAkaCKvvc