Attach (recommended) or Link to PDF file here:

Configuration:
- Web browser and its version: Chrome 90.0.4430.93
- Operating system and its version: macOs Big Sur 11.2.3
- PDF.js version: 2.7.570
- Is a browser extension: No

Steps to reproduce the problem:
1. Load the attached pdf in https://mozilla.github.io/pdf.js/web/viewer.html
2. Go to page 46. Dotted lines are missing in the graphics (see screenshot from acrobat reader)

What is the expected behavior? (add screenshot) See the screenshot
[Technical_Guide_UK.pdf](https://github.com/mozilla/pdf.js/files/6413001/Technical_Guide_UK.pdf)
![Screenshot 2021-05-03 at 07 46 09](https://user-images.githubusercontent.com/3785784/116844541-a343fd80-abe3-11eb-94c3-d03b3dfd6769.png)

scaleX = drawnWidth / MAX_GROUP_SIZE;
        drawnWidth = MAX_GROUP_SIZE;
      }
      if (drawnHeight > MAX_GROUP_SIZE) {
        scaleY = drawnHeight / MAX_GROUP_SIZE;
        drawnHeight = MAX_GROUP_SIZE;
      }
      let cacheId = "groupAt" + this.groupLevel;
      if (group.smask) {
        
        cacheId += "_smask_" + (this.smaskCounter++ % 2);
      }
      const scratchCanvas = this.cachedCanvases.getCanvas(
        cacheId,
        drawnWidth,
        drawnHeight,
        true
      );
      const groupCtx = scratchCanvas.context;
      
      
      groupCtx.scale(1 / scaleX, 1 / scaleY);
      groupCtx.translate(-offsetX, -offsetY);
      groupCtx.transform.apply(groupCtx, currentTransform);
      if (group.smask) {
        
        this.smaskStack.push({
          canvas: scratchCanvas.canvas,
          context: groupCtx,
          offsetX,