The community team just completed changes that merge discussions from the Data Prep forum to the Platform forum. Merging these discussions into one forum will make it easier for you to find and join discussions and ask questions about the DataRobot platform.
The September newsletter mentioned this upcoming change:

Now, you can find all platform questions and discussions in one place: Ask > Platform. The other Ask forum, AI Cloud Platform Trial, continues to be the place for AI Cloud Platform Trial-specific questions and discussions.
If you have any questions or concerns about this change, or find any issues, please send them along. You can just comment below or send email to community@datarobot.com.
Thank you!
DataRobot Community team