When running queries in the editor, it will give an "ORA-03113: end-of-file on communication channel" error. It seems to happens when querying larger datasets. It is consistent when it does happen.
This error is likely caused by a network connectivity issue between Toad and the database.
Please discuss the issue with your company's network administrator. It is likely there is a firewall or some other communication issue preventing the queries to be executed correctly. Check if there are network time out or idle settings or packet size limitations.
Test the issue on other computers on the network. Test various situations, i.e. different databases, logins, and privileges. Temporarily disable local and network firewalls to see if it resolves the issue. Be sure to note all network layers between Toad and the Database, such as Virtual Private Networks, Anti-Virus, Firewalls, and other network settings such as idle time out.
Upgrade to the latest version of Toad at https://support.quest.com/Search/SearchDownloads.aspx. Make sure the database is updated with the latest patches. Make sure the client is current and compatible with the database version.
This may or may not be specific to larger queries/dataset returns.
For Oracle connections:
There maybe a specific command on the firewall called 'inspect sqlnet'. This is known to cause significant connection issues with Oracle. The network and systems need to be configured to allow Toad.exe to pass SQL statements to and from the Oracle database.