We haven't received any reported issues similar to this one, billing9.
Unexpected behaviors or errors in QBO are usually caused by the stored files in your browser. When you visit different sites, it keeps the files on your cache so you can easily load the pages next time. If the cache is holding too much data, it can affect the browsing performance of the currently opened sites like QBO.
You can follow these steps to get rid of the error:
Please let me know if you're able to save the invoice after trying out these steps. Thanks for dropping by.