You don't fix the tweezer with the fan when you apply it on the natural lash.

Your lash adhesive has too long dry time.

Unsuitable environmental conditions. You can use a thermohygrometer to monitor the microclimate in your lash studio.

Your technique isn't good enough. If the fans fall apart very often, perhaps you don't press enough or press the tweezer too strong.

Your tweezer is dirty. Residues of adhesive and another "garbage" can gather on the foot of a tweezer.

You use a bad tweezer. It has a poor closure, an unsuitable shape, stiffness or material. Also, the tweezer can be blunted.

You immerse the fan in lash adhesive too deep.