
Certified GKH Gardening Expert
Depending on what country you are located in, and the climate there, this can be caused by a few things. It is no cause for concern, however.
Lupines flower during the long days, which we are waning from. As flowers start to fade and drop off leaves will start to grow again for the vegetative cycle in preparation to flower next summer.
If this was planted recently, it could have been forced to flower, then changing its environment quickly can shock it a bit forcing it to revert to a vegetative state again.
This article will help you to care for these: https://www.gardeningknowhow.com/ornamental/flowers/lupine/growing-lupines.htm