1. Sounds like a mountainous area, so could be from windshear generated from the hills. Windshear is a rapid change in the speed/direction of the wind. The aircraft relies on airflow over the wings, so if it suddenly experiences a change in the wind, it can be like losing 30mph of forward speed, so losing lift, it can lose altitude. In severe cases, it can lead to a full stall, which is why we try to avoid it.
Coversely, it could gain the speed/altitude.
Aircraft weather radars can predict most windshear, and using these, coupled with good weather forecasts and our experience, we aim to steer clear.
2. An aircraft can "Miss the approach" for a number of reasons:
a. No landing clearance
b. Not seeing runway
c. Vehicle on runway
d. Windshear or crosswind
A multitude of other reasons.