On the bright side, the screen is protecting the pump from chewing this debris into smaller pieces that travel out into the hydraulics.
On the down side, there are bearings and gears that are bathed in this same oil without the protection of being filtered.
I would flush the system, and after a few hours, check the suction screen again. Repeat this process until there is minimal debris found.
It seems that there are transmissions assembled without proper care taken to be sure the castings are clean before assembly. Luckily, mine had none of this debris at the 50 or 400 hour oil changes.