Hello everyone,
Just sharing my 2 cents but I’ve noticed that the rendering device lost error comes as soon as my GPU hits a certain temperature (you can show the temperature of your GPU on the top left part of the screen in the game(go through the options of the game 
)).
This is why setting the game to a lower graphical setting/refresh rate changes the occurence of the error. (at least for me)
Now if you happen to have a 1080Ti or a bigger card and you want to play with settings maxed out you can use an utility like MSI Afterburner to downclock a bit your graphic card (especially if you have one that is factory overclocked like mine).
What I personally did is the following:
Install MSI Afterburner, then in the main window only change the value that is next to “Core Clock” and put a value that is LESS THEN ZERO (if you put a value that is positive then you will overclock your card and that could lead to hardware damage, please be careful !)
example: https ://imgur.com/a/DEdcLvh (remove the space)
Once the negative value is set, click on the “Apply button”
https ://imgur.com/a/3hfXUwe
Test the stability of overwatch by maxing out the settings. (to do this, I personally launch a Practice range and I leave it be for like 15 minutes)
Once you have found a negative value that is stable enough for your card, in MSI Afterburner click on the Windows logo at the bottom left to apply this configuration at the start of your windows.
I’ve had a rock solid Overwatch for months since I did this .
Please also note that since this is linked to your GPU temperature, if the room in which you are playing is hotter than usual then you might need to change the negative value in MSI Afterburner.
Also please note that in practice your GPU will run under his full theoretical potential (since your are downclocking it with MSI Afterburner), but is it worth having a GPU that is unstable when used at his full potential?
Hope this helps the persons having this problem .
Stay safe and heroes never die!