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Its really hard to analyze a traffic drop like this without some critical information about serps. The main guess here is that some high traffic ranking just dropped, that's why im asking about the SC information. And yes, some of all of these issues combined can cause the traffic drop. I'd try to use the analytics information looking for some specific item, such as a page what recieved a lot of traffic and then stopped recieving

Hey Tom! How are you?! The canonicals on your example may have had a brief disappearance, however please look at the below exaple where the canonical was implemented but ignored, http://webcache.googleusercontent.com/search?q=cache:02443r6Ooc8J:www.britishbraces.co.uk/braces/runner-end/runner-end-trouser-braces-wine-5611.html+&cd=84&hl=en&ct=clnk&gl=uk

Hi Lewis, Firstly thank you for taking your time to respond in depth to my question. Since reading your response, I have done the following... Identified the parameters that should NOT be indexed, these are; 'brand=', 'min=' and 'max=' The colour filter 'colour=' is to be kept indexed. I have reviewed the website and found that users cannot currently select to filter more than on colour, which eliminates Google from indexing multiple colour filters in one URL. However, users can still filter by colour and brand, hence why I have requested ours devs to meta noindex any URL that contains the 'brand=' parameter as well as any URLs that have the 'min/max=' parameters as these are price filters. I have also requested rel=next/prev to be implemented correctly. The above should drastically reduce our indexed content. As well as this, I have added the following parameters into Search Consoles' URL Parameter tool as 'No Crawl', 'brand, min, max' -  although I understand this is not a guaranteed fix, it was my first option with no immediate dev time over the weekend. Now the only URLs in need of a canonical is the colour filtered URLs as 'brand, min max' are all noindex. I have asked dev to ensure the canonical points back to page 1 for now, however I am looking into a view-all page option so the canonical would point to that. A good learning curve all of this!