If I had to guess, I'd say your Oracle database connector isn't passing that information back. I'd look for a different database connector or see if you can configure the connector you are using to pull in tables and stored procedures.
Or it may be that your Oracle connector is for a different version of Oracle than you are running...
It could also be permission related.
My next steps would be to reach out to the supplier of the Oracle connector and/or load up a trace on the Oracle database to make sure that you are connected to it as the user you think you are connected as and verify that user has the required access.
Now, on a different note, I never used the table/stored procedure from a dropdown for SSRS - I always TSQL to write up my query as then all control is in the SSRS package. If you are selecting the table from the dropdown, that is similar to using a SELECT * on the table which is something I would avoid in SSRS as it is a performance issue. There are pros and cons to using stored procedures mind you such as changing the stored procedure does not require you to re-deploy the SSRS package. I find it easier to test the changes when it is contained inside the SSRS package mind you. If the stored procedure is used in multiple places and gets changed, it is a lot more testing to ensure that it didn't break anything and some testing MAY get missed.
Just my 2 cents...
The above is all just my opinion on what you should do.
As with all advice you find on a random internet forum - you shouldn't blindly follow it. Always test on a test server to see if there is negative side effects before making changes to live!
I recommend you NEVER run "random code" you found online on any system you care about UNLESS you understand and can verify the code OR you don't care if the code trashes your system.