Attach (recommended) or Link to PDF file here:
https://s3.eu-west-1.amazonaws.com/scai-dev.website.com/tmp/8ab8b56a-fa91-11eb-8d74-0242ac110004.pdf

Hi,
Please see an incorrect canvas rendering for the following document - page 9 specifically. It reproduces on https://mozilla.github.io/pdf.js/web/viewer.html (tried with Chrome). Other pages in this document look pretty much the same but the problem is on page 9 only.

Original screenshot:
![image](https://user-images.githubusercontent.com/23075641/129066656-7bb2fb56-2b88-4f40-8e67-b95bdeb9e521.png)


PDF JS:

![image](https://user-images.githubusercontent.com/23075641/129066734-56503a5c-413c-49c1-9e1c-470da3a642ed.png)

const groupCtx = this.ctx;
    this.groupLevel--;
    this.ctx = this.groupStack.pop();
    composeSMask(this.ctx, this.current.activeSMask, groupCtx);
    this.ctx.restore();
    this.ctx.save(); 
    copyCtxState(groupCtx, this.ctx);
    
    this.current.resumeSMaskCtx = groupCtx;
    
    
    const deltaTransform = Util.transform(
      this.current.activeSMask.startTransformInverse,
      groupCtx.mozCurrentTransform
    );
    this.ctx.transform.apply(this.ctx, deltaTransform);
    
    groupCtx.save();
    groupCtx.setTransform(1, 0, 0, 1, 0, 0);
    groupCtx.clearRect(0, 0, groupCtx.canvas.width, groupCtx.canvas.height);
    groupCtx.restore();
  }
  resumeSMaskGroup() {