Hi!I’m working on panda3d-1.10.15. I have a character model converted from fbx to gltf, which includes a morph animation implemented with shape keys. However, when I load this model using the gltf-viewer or other methods and try to use the animation, the model fails to display normally, and there is a warning: linmath(warning): Tried to invert singular LMatrix4. When I perform the same operation on a cube, everything runs normally. Please help me, I really need this feature. Because,I was new,I can`t upload my model
Greetings, and welcome to the forum! I hope that you find your time here to be positive! 
As to your question, generally the error that you describe is a result of a scale (or component thereof) being set to 0–whether directly or indirectly.
For example, if your animation scales the model along its x-axis, and takes that scale all the way to 0, then you could hit this error.
Or, in a more complex scenario, if your model already has a scale of 0.5 on the y-axis, and your animation reduces its scale on the y-axis by a further 0.5, then you could end up with a scale of 0 on the y-axis and thus encounter this error.