Your page starts starts off with this —> Multi-Award-Winning Digital Agency <— but Google has looked over the page looking for content relating to such comments and failed to find the information on Multi-Award winning.

Maybe this is why your ranking has declined, could this be Achilles heel?

Visually check over the sitemap.xml page yourself and don’t rely on a tool for this to locate the problem. I was adding to my sitemap and noticed a spelling check error only yesterday. Maybe you should show the actual sitemap page

Your metas are the problem here, the title tag is set incorrectly to what’s on the page hence no impressions

Have you considered that you may have encountered an Google HCU, I would monitor the ranking a tad more and if it continues to drop then an HCU might be the problem.