Several technical SEO issues can affect a website’s performance. These include crawlability issues, such as improper URL structures, duplicate content, and thin or missing meta tags. Additionally, problems with site speed, mobile-friendliness, improper canonicalization, and issues with indexing and sitemaps can impact SEO. Addressing these issues involves various strategies, including optimizing website structure, implementing redirects, fixing broken links, improving site speed, ensuring mobile responsiveness, and utilizing proper canonical tags to consolidate duplicate content.