What you see here is automatic triangulation. You have quad faces in your model that are not planar and polygonal faces that are not planar cannot be printed so they are triangulated and since there is no way for a computer algorithm to determine where to insert the edges it sometimes fails to guess.
The solution would be to enter edit mode with your ...
If you need the quads to be planar
The cap-quads can be planar and symmetrical only if D is brought into the plane defined by ABC, in which case the cap is flat, or B is brought into the plane defined by ACD.
One way of taking the second option would be to create an equilateral triangular pyramid with the desired pitch, and looking straight down Z, Knife ...
glTF is a last-mile format. It stores its mesh data in a ready-to-load-onto-the-GPU kind of state.
But the graphics hardware doesn't want the same vertices that artists want to see in Blender. At the hardware level, there are "vertex attributes" for things like normal vectors, UV coordinates, etc., that must be specified per-vertex, not per-face. ...
I've managed to solve the issue over at the Unreal forum.
I did add a simple Armature and did not change the default name. That was the problem.
Change that name to anything but "Armature" and everything works fine.
I solve the problem by using OT Animation Video Codec, then import to Photoshop with transparent background. But there is still another problem, I have set the display and hide some fields in grease pencil, but the video cannot display properly.
In general, the format should not matter as each is supposed to bring the same data into Blender, as long as the format is supported. The unwrapping though does not depend on the format.
Not that format does not matter, but it really has no influence on the unwrapping, as that is based on the geometry that is generated from the data read in/generated inside ...
If you're still after an answer, I have found a few different soloutions to various Blender>Unreal problems that when I combine, seem to work. Could be one of these:
Don't have fullstops in your bone names
Rename your Armature to anything else
Don't call your root bone 'Spine' (You've not done this. Could jut need to be carful eitheir way.)
Not sure if any ...