It may be too wet. If you squeez the shredded paper or castings water shouldn't really come out of it. Maybe a drop or two but not much. If it's too wet you can mix in dry shredded paper in small amounts. If there is any smell then it's gone anaerobic and that can drive out the worms. Once the conditions are right most of the worms will hang out in the compost.

In general I dry my castings some before I use them. It's just so they sift better and I can collect the small worms and cocoons.

Could be the moisture level but worms will move around . I dont know what system you have but with the factory 360 which I have there is a worm elevator so that worms that end of in the drain tray of it happens to be too wet they can climb back up into the next tray. I will add Ive been using mine for 3 yrs now and I find it to be quite efficient but there will be some castings and worms in the drain tray on occasion which I consider normal. Also people that sell these systems will tell you the worms will move from one tray to another which they will do , but they just dont tell you that not all worms will move out of the harvest tray. There will always be some worms in the harvest tray even when its ready. That is also what I go by to harvest the tray, when there is a small amount of worms in that tray I will harvest it.