I downloaded the latest update, today, 9/3/2019, and now my framerate has dropped from a smooth unbroken 30 to a 15 to 14fps. This update clearly breaks the emulator somehow!
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.
What are your specs? Screenshot speed, fps and frametime counter in the bottom right.