I think the problem persists after upgrade your system. Did you try to remove and them reinstall your Redmine stack?
We have a Support Tool that will gather relevant information for us to debug the issue. Could you please download and execute it in the machine where the stack is running?
These are the links to download the tool.
If you are using a console, just type the following to download the tool:
wget -O bnsupport_tool LINK_OF_THE_TOOL && \
chmod +x bnsupport_tool && \
Note: Remember to change the placeholder LINK_OF_THE_TOOL for the link related to your operative system.
The output of the execution of this tool will be a zip file with all the information inside. Could you please send it to firstname.lastname@example.org ?
If you are working with a remote instance and you do not know how can you download the zip file from your instance, you can follow this guide to download it.