Hmmm, for some reason I can't seem to see the video you attached. Maybe it is showing on your end, but on mine it looks like the following screenshot:

So could you please send us that video via email?: contact@esotericsoftware.com

Note that even if the video clearly shows the problem, it always helps to have a written explanation. Since a lot of people will be referring to this forum post by finding it through a search, it would be very helpful if you could write a description of what is going on, so that people experiencing similar problems are more likely to notice the existence of this thread.

yugutou Thank you for posting the video again! I was able to view it successfully. Perhaps this is a known bug. Here is a ticket to fix this issue:
EsotericSoftware/spine-editor806
It has been a long time since we first discovered this problem, but unfortunately the process of moving bones between skeletons is so complex that we have not yet been able to fix it.
This issue occurs when the child bones of the selected bone have slots and are moved to another skeleton, so the workaround should be to make all slots direct children of the bone being moved and then move it. We apologize for the inconvenience and hope you will try that workaround until a fix can be made.

yugutou Thanks for reporting this! I am sorry to hear that the workaround I suggested did not help. I think editing the skeleton data output in JSON format to merge skeletons is a valid workaround, so I hope you can use that for now.