Here are two problems:
1. Vector2 is based on float, and it just doesn't have enough accuracy on a large zoom.
Use doubles or OnlineMapsVector2d instead of Vector2.
OnlineMapsVector2d also has a Lerp method.
2. Use Lerp for coordinates is not correct, because the coordinates exist on the sphere, and the map is displayed on the plane (has a Mercator projection).
For a larger zoom you probably will not see this problem.
But for small zoom it will be very noticeable.
The correct way is Lerp tile position.

Vector2 newMapPos = Vector2.Lerp(pos1,pos2, t);
double longitude = newMapPos.x;
double latitude = newMapPos.y;
OnlineMaps.instance.SetPosition(longitude, latitude);

The map is very zoomed, and I can see that it "shake" a little.
Obviously with a lower zoom is much less noticeable.

Am I doing something wrong or it is normal?
Many thanks