50MB is probably too large for the text editor that is used by default for JSON CLOB's. You can try the following:

1. Query a record with a smaller (or null) value.
2. Click on the cell button to invoke the Large Data Editor.
3. Click on the "External" tab.
4. Enter .json in the "File extension" field.
5. Select an external application to edit the json file.
6. Enable the "Execute automatically next time" option.
7. Press OK.

Marco Kalter
Allround Automations