Symptoms

White or blank screen and no error in the logs after upgrade.

Cause

1. Bitbucket Server Installation files might be corrupted. 
2. Bitbucket Server has a misconfigured server.xml.

Resolution

1. Download the latest Bitbucket Server installation file and unpack it to another directory.
2. Make sure you have the server.xml configured properly according to Change the port Bitbucket listens on. For Stash 3.8 (and future versions) the server.xml file is located in the <bitbucket server home directory>/shared directory. You need to manually update your custom configurations in shared/server.xml for the upgrade to Stash 3.8 or later, as described in here.