Adding the two items your checklist asks for.
Expected vs actual: I expect an imported glTF clip to loop when loop_mode is set. On Godot 4.5.1 (Linux, headless, Forward+), a clip whose glTF declares no loop imports as loop_mode=0 (LOOP_NONE), length 1.0s; the AnimationPlayer plays once and stops at position 1.0 with is_playing=false, and the rig jumps about 12 degrees across the last-to-first frame seam.
Minimal non-confidential example: yes. A small self-contained Godot project I built and validated (quad.glb + its .import + probe scripts + Khronos glTF validator output). Ready to send once scope is agreed.
One extra from the same build, not asked for: 4.5.1 --headless --import never returns on a skinned GLB with a cyclic node graph (a joint that lists itself as its own child; Khronos validator reports NODE_LOOP). The same file with the loop fixed imports in seconds. That looks like a hang that should be an error, not a stall.
Happy to agree version, one issue, deliverables, date and payment. Card link ready.