Thank you! Now I understand Construction Script! I’ve tried your schema into the last official version UE 4.26, and it’s working exactly as on your gif screenshot. I mean, bg-box change its size according to the text size! Nice! But, I have the same issue as you show — flickering characters and keep deleted chars. What could be that? 
In Emulation mode, there is nothing bad. But working in Edit mode is annoying and makes any text job very complicated.
Unfortunately, I can not use this approach in my special version of UE. I use Pixotope UE, and they have removed the original Text3D and paste their own version of the 3d text actor… It works a bit differently. For example, I don’t have the flickering issue but I can not get the text bounding box at the same frame when I change the text. I have to wait until the next frame. Probably, I just have to use Event Tick. 
Is there any way to wait a little bit (next frame) in the Edit mode? Like “Delay” but working everywhere.
Or, force re-rendering the object? Just wondering…
