Possible common causes are the following:
1) There is a bone or slot that is hidden and it has the key on the last frame of the animation.
2) A bone or attachment in a skin has the key on the last frame of the animation, but the skin is not active.
You can quickly find the key that is causing the issue by doing the following:
1) Press ctrl+H
to Show All Bones/Slots
.
2) Check Show all skin attachments
in the tree properties to show timelines for all attachments in all skins.
3) Uncheck Hide viewport skin bones
in the tree properties to show all skin bones. Please note this is not recommended usually, so you should recheck it as soon as you find the bone that is causing the problem.
I hope this will help you.