Using a bunch of crutches, I managed to relatively fix the reference model. But the problem still exists — the bones, especially noticeable on the arms. You said to check the names of the bones, their quantity, but everything is fine with that. Especially in A-pose, you can see that my legs, arms, and neck are deformed. I'm definitely doing something wrong.
Could it be a problem that in Blender the rest position is an A-pose, not a T-pose or something like that?