One of the things you are doing has an onvalid animation.
When it goes back to A or T pose its usually that.
Check your log. Any time the montage or animation fails that way there is a soft error (warning) associated with it.
If you are not, you should be using the copy pose node in the ABP for the death state.
If you are, then maybe something with that node is wrong.
Though you can, and hack wise it is a lot better… if you are switching ABP on the fly you have to make double sure you are loading/unloading correctly.
There’s a forum topic where we users explain how that’s supposed to be done in relation to ladder climing. Take examples from that.
If you arent stitching ABP on the fly, then definitely add a dedicated state machine for death and make sure it has the right animation for the correct skeleton.