How to correctly use kivy graphics context instruction

Hi I recently tried my hands on kivy graphics, context instructions(rotate, ranslate etc). So i tried to implement an animated spinning wheel(used for example to show loading screen). I used garden.iconfonts package for this purpose following closely the example implemented in the package. Heres my code

.kv

<Convert>:
   pos_hint: {'center_x':.5, 'center_y':.5}
   size_hint: .8,.4
   auto_dismiss: False
   on_open:
      self.load()
   loading:loading
   BoxLayout:
      pos: root.pos
      canvas.before:
         Color:
            rgba: 1,1,1,1
         Rectangle:
            pos: self.pos
            size: self.size
            source: 'icons/olivine.png'
      orientation: 'vertical'
      Label:            #STATUS 20 PERCENT
         text: 'Converting file...'
         id: status
         size_hint: 1,.2
         markup: True
      RelativeLayout:    #picture or rolling 60 %
         size_hint: 1,.6
         Label:      #SPINNER
            text: '{}'.format(icon('icon-spin6', 32))
            size_hint: 1,1
            markup: True
            p: 0
            id: loading
            canvas:
               PushMatrix
               Rotate:
                  angle: -self.p
                  origin: self.center
                  axis: 0,0,1
               PopMatrix

.py

from kivy.uix.modalview import ModalView
from kivy.properties import ObjectProperty
from kivy.animation import Animation


class Convert(ModalView):
   loading= ObjectProperty()
   def load(self):
      anim = Animation(p = 360, duration= 1) + Animation(p=0 , duration=0)
      anim.repeat = True
      anim.start(self.loading)

From my code Convert is a popup that shows up when a button is clicked, then as it opens, shows the spinning wheel. But when i run the code it just shows the wheel(i.e the iconfont), but does not spin. The code only works when i change the canvas class under the Label, to canvas.before. I assume that my understanding of how to use these tools is still poor. So im hoping someone can help clearify what im doing wrong, and how to make this work using canvas