.mov to webm not keeping transparent background, transparent background not staying transparent.

[TheeNannigans]

I was trying to create my own twitch alert overlays. 

Started off with a PSD - 750 x 250 pixels. No artboard, transparent background. 

• Imported file to AE as footage. Composition - Retain layers, editable layer styles.
  • Composition added to render queue, double checked transparency by toggling transparency grid. Confirmed.
    • Output module: QuickTime
    • Channels: RGB + Alpha
    • Format options: Animation
  • Used convertio.co to convert from .mov to WebmVP9

Please check attached photos. 

I then went and uploaded completed Webm file to streamlabs to use as follower notification. Black background still remains. 

Someone please tell me where I went wrong, I do not understand where I went wrong. There are no files aside from a logo and text, I made sure to delete the background in the PSD just to make sure as well. 
I have made sure I was using the alpha channel and exporting the alpha channel, I have double checked for transparency using the transparency grid in AE. 

I am using Adobe AfterEffects 17.0.6.

Someone please help. To me this doesn't make any sense. 

[dobbiedo]

Facing similar problem, prores 4444alpha when converting to  webm doesnt retain alpha, even though in ME output says  alpha. Using older version of ME because the latest one doesnt even show option to include alpha.

[pietrol43297977]

mee too.. did you solved?