Unwanted drop shadow after conversion

Thanks, but I'm aware of that. As in the original post, *disregarding* the difference in resolution of the images shown, the blown up image on the right shows a drop shadow that isn't on the original vector. It's only blown up because the original is very small and this enables you to clearly see there is a darker shadow when the original is one flat colour red. It is not representational of the quality of the end result. No effects have been applied.

I've had some progress in finding out the issue. It seems to be an H264 issue. When I export using Quicktime/Pro-res 422, the shadow is gone! My issue is that the client NEEDS the output in H264. Another issue I am now experiencing is that I have two sizes of the same artwork. One is 1080p, the other is 1680x675. The 1080p one is crisp in terms of output quality, the other version is blurred all over. Is this some issue with Animate not processing odd sizes properly?

The SWF file is perfect. It's the conversion to the final required file format that seems to be causing the problems (.mov, H264 encoded). I can't work out how to maintain the quality. Exporting to Video/Media in "Quicktime/default (Animate)" format creates a file for a 10 second basic animation of around 1GB! Running that in Quicktime player, it already shows the drop shadow. I've tried just about every other export option and it's exactly the same. What I usually do after that is run the .mov file through Movavi Video Converter which then chops the size of the file down to around about 10MB (100th the size). I thought that maybe that last step is what was causing the poor quality, but it's the initial export from Animate that's causing it. I'm fast running out of ideas!