Going from Source to wrangler multiple times wrangling different data produces inconsistent results.
Scenario to reproduce:
1. Use BQ source in wrangler
2. Select a table (Ex: customer)
3. Click on Create a pipeline
4. From the studio click on wrangler button
5. In the workspace choose another table (Ex: employees) which has different schema
6. Apply the changes
You will notice that the source is left intact with Customer table and the output schemas after wrangler will be from employee table.
If there are a lot of tables with similar schemas, this will cause un-intended consequence.