After Genji finishes his DragonBlade there is an animation to sheath the blade.
If you continue auto attacking or using other abilities the animation keeps getting reset/queued until you stop attacking.
A fix for this would be to remove the animation from the queue if 2 seconds or more have passed since the ultimate ended.
Hey there! I’ll take a look at this. Thank ya! 
Thanks for the prompt response, I’ve uploaded a video in Try Mode showing how to recreate the bug.
https://imgur.com/a/Fpz4pSV
As you can see Genji attempts to sheathe the DragonBlade several times, but only when I stop autoattacking will the animation fully play out and stop being put back in the queue.