Every season change our lashes go through a slow or faster growth rate. Our lashes take about 60-90 days and you typically shed every day about 1-5 natural lashes. While this is normal, seeing more shedding around fall and spring is also normal. There is nothing to fear with seasonal changes. You will notice more shedding around springtime and autumn, this is normal.
Excessive shedding during season change is normal and not a cause for concern. If you see a natural lash attached to the extension it was that lashes time to shed. If you see an extension without a natural lash on it then the bond was broken or weakened and it popped off most likely.
You will begin to notice your lashes growing faster during spring/summer and slower during fall/winter. Summer weather can cause some clients' skin to sweat and produce more oils which will affect retention, and Winter weather with its lower humidity levels can cause lashes to become more brittle and fall out easier.
When they say beauty is only skin deep, they aren't kidding. What you put into your body is what your body will put out. Maintain a healthy lifestyle inside and out to keep your lashes growing strong, and remember hormones can affect your lash growth. During pregnancy you will see excessive growth and shedding due to hormone levels, vitamins, etc.
Weather is a key part of retention as well. When moisture in the air interacts with uncured adhesive, it can cause the adhesive to react prematurely, weakening the bond between the lash extension and the natural lash. Rain poses a similar threat; getting the extensions wet within the first 24 hours can disrupt the adhesive's setting process. If it is raining out use an umbrella from car to appointment and back to ensure they stay dry.