Strange.
Some options:
The trigger is bent/broke, or the trigger spring is broken or displaced, allowing or forcing the trigger to stay to the rear.
Something is wedged or jammed in the action around the trigger. Look for grit or bits of metal.
You don't have the receivers assembled correctly or the thumb screw isn't snugged down.
Check the receivers on the left side to insure both halves are fully seated. If there's a "step" in the joint area, the receivers aren't seated together properly.
Make sure the thumb screw is snug but don't over tighten it. Just snugged down is plenty. Use a quarter, not a screwdriver. A screwdriver will "dink" up the screw head.
The lever screw is broken and allowing the lever to shift forward. In this case, I'd think that the rifle wouldn't operate and it'd be obvious.
