Hi,
Sometimes when i check out of the game in the main menu or at the end of the game for some messages on discord or just online the game tends to freeze when i tab back in. The only fix for this is to restart due to this i’ve also noticed that i lose Endorsement levels because apparently it counts or something. Out of nowhere i went from 4 to 3 and even when the game is just finished and you tab out or you just press go back to main menu your endorsement levels go down too… Which is quite strange…
Is there a fix for this that doesn’t make me lose endorsement levels?
Hello ButtonSmash,
Keep in mind that your Endorsement levels do decrease if you are not receiving new ones or if you leave the games before they’re finished.
You can find more information here. 
As for your Alt+Tab issue, please check if it persists if you close all unnecessary background applications (everything your system does not need to work properly), overlays especially!
Feedback? Click here! Blizzard EU - Customer Service Forum Representatives Surveys - Vyraneer
Well thanks! But if your game crashes i can’t do anything about it!
A game crash can be caused by many different causes. Please, start by following the instructions given by Vyraneer in her message above. More often that not, those crashes when alt-tabbing are caused by other programs (specially those with overlays) causing conflicts.
If the issue persists, there are some more things you can try.
Make sure both your operative system and drivers are up to date:
battle.net/support/article/31024
Make sure you deactivate Xbox DVR:
battle.net/support/article/92046
Delete the Battle.net Cache folder:
battle.net/support/article/34721
Repair the game:
battle.net/support/article/7655
Got feedback about the support I’m providing? Leave your comments here!