The root bone has Y-Axis animation on it in the preview, but not ingame. Why?

The rig of my character (made in Blender) has a simple running animation and this shows perfectly in the preview window. But when I play it ingame the root bone is just stuck in place, which looks really weird. I've spent hours looking for answers on Google and I've had enough by now, if there actually is a thread out there discussing this topic please show me. The rig is marked as Generic in the Rig tab, no Root node selected. In the Animation tab I have Loop Time and Loop Pose checked, I did not touch any other settings. (I've tried messing around with the settings A LOT but i did not ever get any result except that the character turned sideways and ironically played the animation perfectly...)

Could you please tell me how to set this stuff up correctly? I just want the root bone to go up and down when the character runs, anything else looks weird and buggy.

Edit further information on my current setting: The rig looks a bit humanoid, but it doesn't correspond well to the humanoid system because of proportional distortions and additional bones compared to the "perfect human rig" (that's why i chose generic). The root bone is at the hip, with y-translation animation only. The hip bone itself, directly attached to the root bone, has rotation animation. Avatar option is "Create from this model"