You won't be bumped for someone with more status or LPs.
A few possibilitiies are
- Equipment swap - Aircraft type change. Sometimes, the system glitches and reassigns seats even if the swap is to the same type. Someone may have been looking and snapped up 9D
- Broken seat - Unlikely this early though
- FAM - Air Marshall. In which case, you're stuck.
You can call AA and ask if they can see anything. If it is #3, they can't/won't say anything.