When you create a task from Zapier/Email to Marvin, you can use the # shortcut to specify what its parent category/project should be, e.g. #Work. But if you have multiple projects/categories called "Work", then Marvin doesn't know exactly which one you mean and just chooses one.
If you want to target a particular instance, you can use its unique ID directly. In order to find this, first ensure the Deep Links strategy is enabled, then hover over a category or project with your mouse and click the Anchor icon (you may have to click the ... to expand these buttons) to copy the deep link:
If you don't see this button, configure your "Right-click menu" or "Hover button actions" strategy settings to add the "Copy deep link" action to your menu.
After clicking the Anchor icon, the deep link will be copied to your clipboard. If you paste this somewhere, you'll see a link like:
All project/category deep links start with https://app.amazingmarvin.com/#p=, and everything after that (highlighted in the image above) is its unique ID.
Now when you create the task in Zapier or in an Email, use #ID, and then you should find the new task in the correct place: