This is a tricky one— from the description you’ve provided it sounds like everything should work. When you look at your Run History for the automation does it show that the date was input?
If your run history isn’t showing anything suspicious I think contacting customer support here might be the best way to go.
You can send them a short video of your automation run, and they’l be able to help figure out the problem. Also, I recommend checking out our automation troubleshooting guide if you’d like a little more context on how we generally troubleshoot automations.