It sounds like you are experiencing issues with copying and pasting animations in Spine, where some actions become invalid after extending the animation. This can happen if the keys for certain actions are not properly copied or if there are missing keys in the extended part of the animation.
Here are a few steps you can try to resolve this issue:
Ensure All Keys are Copied: Make sure that all the necessary keys for the actions are copied. Sometimes, keys for certain bones or slots might be missing, which can cause the actions to become invalid. You can manually add keys at the frame you want to copy from if they are missing.
Check Key Interpolation: Verify that the interpolation between keys is correct. Sometimes, the interpolation might not be copied correctly, leading to unexpected behavior in the extended animation.
Use Box Selection: When copying keys, use box selection to ensure you are selecting all the relevant keys for the actions. This can help in copying all the necessary data.
Duplicate Animation Clips: As a workaround, you can try duplicating the entire animation clip and then adjusting the timing to extend the animation. This can help in maintaining the integrity of the actions.
Check for Animation Cleanup: Ensure that the "Animation cleanup" option is not enabled in the Export Settings, as it can remove keys identical to the setup pose, which might be causing the actions to become invalid.
For more detailed steps, you can refer to the following resources:
If the problem persists, you might need to manually adjust the keys in the extended part of the animation to ensure all actions are correctly represented.