Lightmap density "disappears" after light baking

[FONT=arial, helvetica, sans-serif]All meshes were treated before imported so there’s diffuse UV and lightmap UV.
In the images I show the density of lightmaps displayed in the viewport, but it’s before any lightbaking, after any bake unreal automatically turn all lightmaps into “0”, “none” or “blue” (I don’t know how to categorize this bug). - I’ve tested with CPU and GPU light baking.

PS: If i just turn on then off any “override lightmap” the density display comes back, and it also happens the same with if I change the Lightmap Resolution number to (e.g.) 255 then turn it back to 256.

Please help me, thank you all