Hello,
Make sure the stem is seating all the way into the movement. Sometimes it may look like it is but not. That little set screw has to seat down in a gap on the stem that holds it into place. Also make sure the little screw did not break, making it too short to reach the gap. Other than that check your reassembly carefully. I don’t know exactly what kind of movement your working on but I hope this will help.
I wish you well 
Jim
