When using a Text Box with multiple lines inside a Retainer, the lines overlap with each other depending on the letters. It doesn't look this way in the Widget Designer. Additionally, it doesn't look this way without the retainer box. You can observe the difference by adding a Set Retain Rendering node after the Add to Viewport node and toggling the In Retain Rendering boolean on and off.
Tested in //UE4/Release-4.25 @ CL 14469661 and this issue did not occur, so marking as a Regression.
The spacing between the lines is different from what it appears like in the Widget BP designer and they overlap each other.
The retainer box wouldn't change the spacing of the text once in game.
There's no existing public thread on this issue, so head over to Questions & Answers just mention UE-114934 in the post.