You need to ensure that when doing your prep you use your 240 grit file to tidy up the free edge of the nail, then when using the Harmony 180 grit buffer to remove the shine from the nail you then bevel the free edge using a downward stroke along the width of the free edge.
Ensure your Foundation Gel is not applied to thickly - it needs to be very very thinly applied & be sure you cap the free edge by running the brush under the free edge. Don't leave a ridge of Foundation on the free edge - swipe down the length of the nail again after capping.
Check your UV bulbs are not old if using a UV lamp. If using the Harmony LED lamp, ensure the fingers are positioned correctly when curing.
If you are still having problems after following the correct prep procedure, perhap attending one of the great value Gelish Training Days in you area would also help. xxx