Yeah they're definitely right, as a whole our canonicals Google agree with, but there's various batches that Google chooses to ignore.
Unfortunately I don't have access to search console, I have access to GA but that's it. I have to rely on third party tools and other things to try and see the impact. We also have a very restrictive platform which requires things to go through development. So i'm just trying to gauge the seriousness of this issue so that I can do a priority list.
To put the scale into perspective, it looks as if Google is ignoring the majority of our product URLs (thanks to a product recommendation software we use) and is using a different url path. Same with breadcrumbs.
255k indexed pages, ignored canonicals that i've found run to about 15k from just the two above.