While reconnecting, the designed table schema name must be same with reconnected table name otherwise it will reset all your dashboard settings.
Besides that, Oracle connection on Dashboard Designer never worked well. I use the dashboard designer since version 2.2..
Also, I have the following error when I'm trying to made the relation of two tables on dashboard designer using Oracle
“There is not enough quota to process this command” exception occurs only when the memory problem arises. So we suggest you to close some applications and ty to increase your virtual memory. Please refer below links,