Some possible explanations that occur to me:
1. You have accidentally changed the steps/mm for the X axis in your firmware configuration. Have you uploaded new firmware recently?
2. The X axis driver has developed a fault. But you said you already tried swapping them.
3. The microstepping configuration has changed, so the X driver is now doing twice the number of microsteps it was previously. I believe the number of microsteps is controlled by jumpers underneath the drivers, which are connected to the 3 microstepping control pins on the driver socket. I guess it's possible that there is a bad connection in that circuit.
1. You have accidentally changed the steps/mm for the X axis in your firmware configuration. Have you uploaded new firmware recently?
2. The X axis driver has developed a fault. But you said you already tried swapping them.
3. The microstepping configuration has changed, so the X driver is now doing twice the number of microsteps it was previously. I believe the number of microsteps is controlled by jumpers underneath the drivers, which are connected to the 3 microstepping control pins on the driver socket. I guess it's possible that there is a bad connection in that circuit.