You may have activated alternative flight controls. I can't remember if this is the default button binding but it is L3 for me
Indeed, i reckon this is what's wrong, though it might not be, but if it is, Mik... is right that L3 switches to alternative controls, which for some reason by default only seems to be lacking in yaw control, but has all the other controls otherwise mapped identically (unless you reprogramme the buttons in either control scheme).
It's easy to accidentally press L3 and switch to the alternative controls during combat, which i've done several times, though the first time, i too thought there was something wrong with my ship and logged out and back in two or three times, before i realised what the problem was...

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So when you get back into the game, even if the problem has reset, try pressing L3 a few times and you'll see the information in the top right of your hud saying that your ship is switching between standard and alternative controls.
With your ship in a safe area, try yawing under alternate controls and nothing will happen, but press L3 again and suddenly you'll be yawing again...

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If that doesn't solve your problem, be sure to tell us

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