When Reverse Engineering some tables in a database, the status holds on 'Reversing Columns' and doesn't seem to complete. Leaving the process to run for several hours doesn't return any data.
This can be related to the Primary & Foreign Key relationship constraints on the table.
When reverse engineering, Toad Data Modeler looks through all of these to find the links, and depending on the complexity, this could be where the speed issue is occurring. Also if there is a loop in the relationships, it could cause this issue.
Check to ensure the Primary and Foreign Key relationships are not causing any loops. If the links are referencing many other tables, this will explain the speed issue.