Ting Please note that Spine 3.8.99 is no longer being updated and any problems found on it cannot be fixed.
As far as I have tried duplicating a skeleton with skin constraints in Spine 4.2.34, the skin constraints are not lost. If you can confirm that the problem is not reproduced in Spine 4.2.34, please consider upgrading the editor and runtime you are using for your project to resolve this issue.

Ting I understand that version upgrades are not easy, but considering that it has been about 4 years since the last version of Spine 3.8 was released, I think it is a reasonable time to consider an upgrade. We encourage you to discuss this with your project team. If you get stuck with a version upgrade or have any problems, we are here to help.