If your Redmine version is not officially supported by the plugin you are trying to use, please uninstall the plugin and restart all services.
Apart from that, we have a Support Tool that will gather relevant information for us to analyze your configuration and logs. Could you please 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 ID that is shown at the end.
Hope it helps,