I had this issue as well. The problem started yesterday for me, and it would usually take upwards of 5 minutes for the game to finally launch. Once it did, it would freeze while loading a new map, but during an actual match, it seemed to work fine. It was when a match ended that the problems began.
What worked for me was to go to Settings > Components > click Customize on File System Shield > Exclusions, and adding the folder where Overwatch is installed, as well as the folder for Battle.net.
For me it was "C:\Program Files (x86)\Overwatch\" and "C:\Program Files (x86)\Battle.net\". I also added the folder for Overwatch Test (the PTR), but not everyone uses that, so I'm not sure if that had any effect~