PlayerStart wont work

If i remove the PlayerStart or Pawn,
after press play game will create
Character Mesh

Makes sense.

if i add a PlayerStart, after i press
Play it create Character Mesh ignoring
the Player Start,

Ensure you have 1 Player Start and no Pawn (which you call character mesh here, I believe)

same thing happen if i add the Pawn in world after i remove
Player Start

This also makes sense.

I created a new map so when i press
Play Character fall undermap

Also makes sense - this could easily happen if you have no Pawn present in the world and no Player Start; the Game Mode will spawn one at 0,0,0 (adjusting locating a bit which it can do) but if that spots is under the map, you’ll fall.