FPS drop and performance problem


We are building an application that requires sensor volume visualization and these sensor volumes are changing their orientation with time. I am using Cesium-sensors plugin for this purpose but there is a problem that I see, when I have a lot of sensors (~15) in the scene, I can observe a significant FPS drop (from 60 fps to 35 fps) and this is causing a performance drop in our application. In order to find out what could be causing the problem I used WebGL Inspector (a chrome extension) to analyse what is happening per frame, and here is what I found out:
- There are a lot of buffer writes per frame even though content of these buffers is not changing. I mean its creating new buffers even when the vertices are not changing.

Why is it creating and writing new buffers if geometry is not changing?
Can someone help me understand why this is happening and give me a possible solution for increasing performance of our application?

I am using Cesium Version 1.6.