The log file is incomplete. Make sure you follow the steps carefully:
Open Citra, then go to File>Open Citra Folder (Citra>Open Citra Folder if on MacOS) and open up the log folder. Now keep that open in the background.
Launch your game and encounter the problem; crash/slowdown/glitch and close Citra if it doesn’t do so by itself. Do not restart Citra as that will wipe the log of important information!