Brilliant diamond save fails

i saved ingame…but after restarting the game i had to play from the very beginning…

In order for us to provide better support, we need to see the log generated by Citra. This guide will walk you through how you can obtain the log file: How to Upload the Log File.

Did yuzu crash after you closed it?
Try this, right click the game and select open save data location, navigate 2 folders back and you will be in the profile IDs, check if you have an older profile and the save should be there, move it to the current profile and it should work.