Frame drops by calling webgl render sub function

I made panorama cube with mesh.

Panorama cube’s 6 each face is textured by loaded image
and mesh is added inside of panorama cube.

When I rotate camera, sometimes frame goes smooth
but sometimes frame goes little bit down.

Which ways I can approach this problems?

It seems you screenshots just show the initial texture upload overhead. This is a single-time issue and does not appear again if you just render your scene.