I was having the same issue, but what seemed to work was setting the permissions to daemon/daemon, then after upgrade reverting back to bitnami/daemon.
Using the following commands:
- sudo chown -R daemon /opt/bitnami/apps/joomla/htdocs
Then after upgrading; whether through the control panel or using the extensions and installing using the url.
You can replace "joomla" with any other name you may have changed it too.
If that doesn't work, try disabling FTP; while still having daemon/daemon.
Seemed to work with a few sites I have with a little fiddling around..
Then revert back to bitnami/daemon; using:
- sudo chown -R bitnami /opt/bitnami/apps/joomla/htdocs/