Changing client on invoice deletes all the data

Hi there, 

Thanks for connecting with us in the Community. It's important you're able to navigate the program without running into issues. Rest assured, I'll be glad to steer you in the right direction. 

When creating an invoice you can change the client without the products and services changing in the line items. That being said, I suspect this may be a browser-related issue that's causing the error you're experiencing. Clearing cache and cookies helps with fixing most browser issues. You can do this by following the steps in this article: Clear Cache and Cookies.

Give this a try and let me know what happens. I'll be here in case you have other questions.