I've Seen this a few times & have to agree with previous posts. When you drop the pan & dont find the band strut, (If it has fallen out ) fish around on top of the valve body. Good chance it is laying around on there.
Front band servo pistons use metal rings, so they never just quit sealing all of a sudden.
They also can't over travel or flip sideways like a rear band servo does.
This is going to be pretty obvious when he see's it, as either the adjuster as backed off so far it skips second all together, or the strut fell out from being too loose, or the band broke.
With the pan off I adjust the band by sticking just the tip of my index finger between the servo pin tip and the band apply lever and tighten the adjuster down till it starts to hurt my fingernail and lock her down. :D
Of course others have smaller or larger fingers.
