That tmp directory is located at /opt/bitnami/php/tmp and is owned by daemon as it's the process that serves the application.
In order to solve indexation issues, I suggest you ask in the official forums of Magento to obtain more information about that.
We have a Support Tool that will gather relevant information for us to debug the issue. Could you please download and execute it on the machine where the stack is running by following the steps described in the guide below?
How to Run the Bitnami Support Tool
Please note that you need to paste the code outputted by the tool in your reply.