That is a very good question! You are not alone...
What version of Photoshop are you running? And what computer and operating system? We will be albe to help yo more effectively with that information.
I don't have a fix for you at the moment, but I have a workaround until the issue is fixed...at the end of the day, save yor patterns into a pattern file and then if they disappear, you can reload them.
After you create your patterns, Select each of them and from the flyout menu on the side of the Patterns Panel, Choose Export Selected Patterns. Save them in the Patterns folder that Opens up, and click save. Then tomorrow if your patterns are not there, select Import Patterns and select the group that you saved when the dialog opens up. This is just a workaround until the issue is fixed.
Here is a list of fixed issues in the latest version of PS 23.1:
https://helpx.adobe.com/photoshop/kb/fixed-issues.html
Michelle