As with any problem, the first thing you should do is contact Cash App customer support. The easiest way to do this is from within Cash App.
To get help from Cash App from within Cash App:
Tap on the picture of your profile in the upper right corner of the Cash App.
Scroll down and tap "Support" at the bottom.
You can try searching for an answer to your question, but since mobile check depositing is a new feature, it is unlikely that you will find much help. Scroll down instead and tap "Chat with support." Type in your question or problem, and someone from Cash App will get back to you as soon as they can (though it may take several hours to get a response).