Here’s a key take-away from John Mueller at Google: canonical tags are case-sensitive when it comes to URL paths & filenames.
URL hostnames (domains) aren’t case sensitive, but if your canonical has /Topic/Article and the actual URL is /topic/article, you’re asking for trouble.
What this means for you: make sure canonical URLs match exactly (including case) the preferred page version. Don’t rely on “hope Google figures it out, hope is not a strategy.
Time to audit those canonicals 🎯