Mineral spirits should remove this but it will probably damage the paint. I can't think of a product that would dissolve that kind of adhesive and be safe for the paint.

Try a hairdryer to soften it and scrape with a plastic scraper - if it's a sticky, plastic type residue.

Thanks all

Come back and tell us the result you had.

I've had random results until rubbing alcohol on different problems with surprising results. Did you know that it removes silly putty from Nintendo Wii drums?

That looks like thinset (cement based) to me. Which would make sense from a heat resistance standpoint also. It's used to bed tile and tile backer board - and your heat shield was probably cement board of some type.

If its thinset, you will only be able to mechanically remove it. There's nothing that will dissolve it. Scrape it knowing you will damage the top layer of the drywall and then skim the drywall with mud.