Please always list the full version number, which is the name of the unitypackage or zip package that you have downloaded. It's also listed in
Assets/Spine/version.txt for the spine-unity runtime, and in
com.esotericsoftware.spine.urp-shaders/version.txt in case of the Spine URP Shaders UPM package.
If you are not using the latest version of the Spine URP shaders UPM package and the spine-unity runtime, please be sure to first try whether updating the packages resolves your issue:
Also please note that version 3.8 is already very old, we have released many bugfixes since then. It's been 25 commits on the Spine URP shaders alone, as can be seen here. Could you please check whether this same issue also still occurs when you are using the latest version of the spine-unity 4.1 runtime and Spine URP Shaders UPM package?