This condition just occured on my 2008 9-3 Aero. When starting off, the transmission seemed to disconnect from drive, (like going to neutral), then re-engage, (rather harshly because the engine RPM increased when the transmission disengaged). Several months ago as routine maintenance, the transmission fluid, (per specification) was changed. The fluid was not terribly dirty and no metal fragnemts were observed. The car has about 93K miles.

 

The problem was low fluid level. Why? The seal on the input / output shaft to the transmission simply dislodged from the transmission housing. Weird this is! There was no cir-clip holding the seal in place, it appears the seal is pressed into the trani housing. I pulled the seal away from the housing, (as far as I could move it), cleaned away all oil and applied "Yamaha Bond" to the edges of the seal and pressed it back into the housing. Refill the transmission and everything is normal.