Technical SEO issues are backend problems that block search engines from accessing, understanding, or ranking your site. They're different from content or link issues because they exist at the infrastructure level, often invisible to regular visitors but critical to how Google sees your pages. The most common technical issues we fix at Ottawa SEO include crawl errors like 404s and 500s, indexation problems from misconfigured robots.txt or noindex tags, and canonicalization failures where duplicate versions of pages compete against each other. Page speed consistently tops the list too, especially Core Web Vitals failures from unoptimized images, render-blocking JavaScript, or poor server response times above 600ms. Mobile usability problems still plague sites in 2025. Think viewport issues, buttons too close together, or text too small to read on phones. Google's mobile-first indexing means these aren't minor annoyances anymore. Similarly, HTTPS migrations gone wrong create mixed content warnings or redirect chains that leak authority and confuse crawlers. Structured data errors matter more now that Google relies on schema markup for rich results. Invalid JSON-ID, missing required fields, or outdated vocabulary can kill your chances at featured snippets or product carousels. We also see sites with broken XML sitemaps listing URLs that 404 or exclude priority pages entirely. URL structure issues include parameters creating infinite crawl loops, non-canonical HTTPS/HTTP versions both indexed, or wwww versus non-www duplication. Hreflang mistakes on bilingual Canadian sites cause the wrong language version to rank in Quebec versus Ontario searches. The tradeoff with technical fixes is they're high-impact but require developer time. A single redirect chain fix might recover 15-20% of lost authority on a key page, but you need server access and testing. We prioritize issues by crawl budget impact first, then user experience, then nice-to-haves. Most sites have 20-40 technical issues at any moment. Focus on the top five that actually block rankings or revenue, not every yellow flag in Screaming Frog.