Toad intermittently freezes while browsing in Schema Browser | Data Tab.
Intermittently, when looking at the details for a table (i.e. data and columns) and selecting another table, the data from previous table remains and/or TOAD freezes and the whole window becomes grayed out. Upon further testing, other Schema Browser windows for other database connections actually still work; only one Schema Browser Window is frozen.
Full un-install and re-install of Toad, including renaming or deleting all 'Toad for Oracle' Program Files and App Data folders, resolved the issue.