Hi pnunez -
We haven’t seen anything reported yet for an issue like this, if you can share your project I can take a look.
Thank You
Eric Ketchum
If you would like to keep them private you can post a link to them directly to me via the Unreal Engine Forums.
Ok, I will post the two versions. 
I hope nobody steals me the project 
I have just send my projects by private message
Hi pnunez -
Your 4.8 Project did not have it’s Static Lighting Built. Once built the 4.8 project matched the 4.9 project identically. To remove the flaring white light, you need to adjust the Min and Max Brightness of your Post Process Volume upwards to something like .5 or 1
Thank You
Eric Kethcum
A year later and found this and it saved my project file. Just wanted to say thanks and reiterate to others that Intermediate and Saved can definitely be the culprit.