Upgrading to 4.7.2, and the process completed, but locked up the site. Had to use recovery mode. details below. It came back eventually, but thought the error details would be helpful.
I updated the theme on my local installation however i did not have such issue and logs are clear. I set PHP version to 7.2.8. As far as i know other users have not reported such issue but thanks for reporting. If the issue re-occurs, please let us know :)