This issue was resolved in a previous version. However Untangle NGFW cannot insert a new encryption into the OpenVPN server automatically on upgrade as it would break all existing VPN clients. So in order to insert the new encryption level you will need to completely remove OpenVPN app from Untangle. Install it again, then rebuild and redeploy all of your OpenVPN clients. Please note that this is a major change and as such requires several steps to complete.
1) Export the existing clients list found under OpenVPN > Server tab > Remote Clients tab.
2) Click Remove OpenVPN in the lower left corner under OpenVPN > Status tab.
3) Click Install Apps and re-install OpenVPN.
4) Import the clients list that was exported in step 1.
5) Download all clients and distribute to the associated users. They will need to reinstall the OpenVPN client.