This would usually happen if the extension has not bonded correctly with the natural lash. It can be because the adhesive has dried too quickly to fully bond. Try to pick up more adhesive to allow better surface coverage. Always isolate natural lash first, then dip extension in to the glue, this helps to get better retention. If humidity higher, always pick up more glue. Even slow drying adhesives, dries faster in higher humidity / temperature then manufacturer noted. Also it can happen if customers haven’t followed the aftercare instructions correctly. If you use nano mister, if you over sprayed this could cause shock polymerization and lashes not bonded properly, they might fall faster, or if clients eyes were tearing during the application.