Hi GermanoGuidi -
Jacky is correct in his question. You are probably using a SceneTexture:SceneColor node which should be replaced with a SceneTexture:PostProcess0 node in a Blendable.
Thank You
Eric Ketchum
After upgrading to 4.9 , they have presented these strange edges , visible both in editor and in game . probably is a problem because of the lights is manifested only in the states " lit " Detail lightning " and " only lightning " .
I 've tried to do the build, but nothing has changed . Thank you in advance
Are you using any post process materials(blendables)?
the only one I’m using is the postprocessVolume to change the overall color
I changed as you said yourself in all materials " blendable " I found ( 3 ) but nothing has changed . I 'm sure something wrong , but many thanks to you both for your help.
Does it still appear if you remove the post process volume?
ok I found the problem .
just like you said you, the problem was changing sceneTexture , and was in material M_Highlight .
Thank you very much and good luck to all 
Thanks guys this had me too. It took me a moment to figure out you have to select the scenetexture to change its scenecolor to postprocessinput0 in the details window
This worked perfectly for me. Thank you for the help folks! Sneaky little scenetexture.
Okey, had the same problem and have discovered where exactly it is.
I installed Chameleon into my scene and updated from 4.18.3 to 4.19.2 and that brick border popped up.
Any of the visual effects I enable or activate from Chameleon, makes that brick border visible again.
Fixed it upgrading Chameleon FX from Epic Games Launcher and replaced all new files.
Now it works fine with no brick texture border. Theres also another way to fix Chameleon, “you should be able to fix this by adding T_White to the two main structs in the Chameleon/Structures folder.”
( Chameleon Post Process - Marketplace - Unreal Engine Forums )