Yo there 
I feel like a complete beginner. Everything is solved now.

The problem was:
- the component "Area Map View" was offset by 1500 / 200 in the MapBackground actor
- I must have moved it by mistake while I was selecting it for discovery reasons (I click everywhere like a madman :x)
It's really silly and I feel a bit sorry for the screenshot spam these past two days when it was so simple!
But! To make it sure nobody makes the mistake again, I suggest you to set the relative position of the "Area Map View" component to 0;0;0 in the Construction Script.
Another thing that bothered me was the weird relative location / rotation of the "Capture Scene Component". I resetted it but nothing was captured after that so I dropped another Map Background just to see what its original Transform. And it is indeed a very weird transform
Maybe you should also add it to the list of things you set in the Construction Script to avoid people from resetting it thinking they have modified it by mistake.
Thank you very much for your support and your time
You put me back on track with your answers (it was in fact the first suggestion of your previous message that made me think of this fix).
I can't wait to try things out now
PS: You can change the color of the Navmesh if your project settings!
EDIT:
Actually I have another question [MENTION=23394]Zhi Kang Shao[/MENTION]!
I rotated the Widget Minimap by -45 Angle (in Widget, tried both the minimap widget directly and a box containing it). Here are the results (the red Arrow is the character):

You can see the Character Icon is offset by an amount on the minimap but everything else works fine!
Here is the widget setup:

I feel like a complete beginner. Everything is solved now.
The problem was:
- the component "Area Map View" was offset by 1500 / 200 in the MapBackground actor
- I must have moved it by mistake while I was selecting it for discovery reasons (I click everywhere like a madman :x)
It's really silly and I feel a bit sorry for the screenshot spam these past two days when it was so simple!
But! To make it sure nobody makes the mistake again, I suggest you to set the relative position of the "Area Map View" component to 0;0;0 in the Construction Script.
Another thing that bothered me was the weird relative location / rotation of the "Capture Scene Component". I resetted it but nothing was captured after that so I dropped another Map Background just to see what its original Transform. And it is indeed a very weird transform

Thank you very much for your support and your time

I can't wait to try things out now

PS: You can change the color of the Navmesh if your project settings!
EDIT:
Actually I have another question [MENTION=23394]Zhi Kang Shao[/MENTION]!
I rotated the Widget Minimap by -45 Angle (in Widget, tried both the minimap widget directly and a box containing it). Here are the results (the red Arrow is the character):
You can see the Character Icon is offset by an amount on the minimap but everything else works fine!
Here is the widget setup:
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