I know this is closed but I have seen this happen with extremely complex enemies and I want to share how I fixed this. If you have sprites that disappear but still are there one thing you can do is make a simplified clone of the object with the exact same animations and then make a for each loop that does a match on the UIDs. Then match the animation and mirroring to the parent UID. This is a good practice anyways as it leaves the underlying object with the gobs of code and the image displayed independent... similar to how you should handle walk... anyways i thought I would share. This issue used to plague me too and now I add a 'married dummy clone' on top and life is good.
This is for anyone who finds this thread and is dying inside trying to fix vanishing complex objects.
Cheers
Dan