Did you tighten the device?
FLEX attaches to the barbell with internal magnets and a locking ring.
The magnets are sufficient for movements where you don't dump the bar, however we use the locking ring for exercises such as a Snatch or Jerk, etc.
• Attach the FLEX device like an end cap to the barbell and you'll feel the magnets lock it into place.
• Tighten the locking ring by using a twisting motion on the device
• Give it a wiggle - it should be pretty tight now.