Sorry, we've got a fix in 3.8.57 and we'll get it uploaded ASAP.
3.8.57 is now up with the fix! Sorry again.
Please note there is a separate problem in the Spine Runtimes for skeletons that don't have any attachments in the default skin
in other words, for skeletons that have all attachments in skins. The fix has been made in the reference implementation, spine-libgdx, and will be ported to all the other runtimes first thing in the morning. Sorry for the trouble!