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I also think this i due to the latest Google update. Many websites have lost their traffic and many post have disappeared even if they are as you say indexed. I would start as mentioned above by checking Google search console, if there are no errors then i belive this is a sign of bad quality content and would recommend to go throw your articles to se if they really give the user what they searched for.

Yes, your robots.txt file appears to be correctly configured for common use cases. Here is a brief explanation of each line to ensure it meets your needs:

Sitemap: https://www.in2town.co.uk/sitemap_index.xml:
    This specifies the location of your sitemap, which helps search engines understand the structure of your site and find all of your pages.

User-agent: *:
    This applies the following rules to all web crawlers.

Disallow: /wp-admin/:
    This prevents web crawlers from accessing your WordPress admin area, which is standard practice for security and to prevent search engines from indexing unnecessary pages.

Allow: /wp-admin/admin-ajax.php:
    This explicitly allows access to admin-ajax.php, which is often necessary for some plugins and features in WordPress to function correctly.

Allow: /ads.txt:
    This explicitly allows access to the ads.txt file, which is used by the Authorized Digital Sellers standard to prevent ad fraud.