Nav Mesh Lighter green colour

I’ve a problem with my Nav mesh it has two shades of colour, and is affecting how my characters are walking from A-B. I’ve been through all the objects on the Outliner, so I don’t think it’s just a random shape in the way, I’ve double checked my targetpoints the characters walk to, to make sure I’ve not accidentally moved or added something in…but nothing.
Any ideas? What does the lighter green patch mean?