Hi,
This is known (I know it is somewhat counterintuitive), but this is how Bump is calculated and how the tile map works.
While TileMap will work fine with displacement, it currently needs to be converted to be used with bump. Using CoronaBumpConverter is a solution here.
More technical explanation from devs:
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Displacement is handled differently than bump mapping - displacement works directly with texture. Bump mapping needs to convert the texture into "Bump directions". TileMap provides just a way how to tile input textures, it does not convert the textures into bumps - that functionality is in bump convertor. If the input textures to TileMap are already bumps, bump mapping will work fine.
"
Specifically to avoid confusion in "If the input textures to TileMap are already bumps, bump mapping will work fine": the bump coming from the input textures will be applied, but not the Tile gaps. Remember, TileMap just tiles the textures and creates procedural map. If you want to have a bump from the map itself you see, you need to convert it by using CoronaBumpConverter.
Hope this helps.
This is, of course, reported and in the future there should be no need to convert the TileMap into bump, it will be done automatically when plugged into material's bump slot.
(Internal ID=1263831503)