Currently i've got products in a category sub of default for example:
Root -> Sub cat -> product
I've noticed that on the product page itself the breadcrumbs are working fine for some products and not for others. Some products will show the category and others wont show the category in the breadcrumb, they will either not show the category or they will show the category.
Something else i have come across is if I currently don't assign the product to default cat the following happens:
The product is assigned to default cat
The product has a sort order of 0 in the category list
The breadcrumbs don't show the category.
What is going on? Why is the breadcrumb breaking when it is either assigned to this Default cat ( which is the root cat btw ) and I don't get what is happening with the products where the category isn't being shown in the breadcrumb.
Magento is on 2.2 - I've reindexed - I've flushed cache.
I've also pulled all of my hair out - no just a joke.
* EDIT *
If anyone is having this issue, Full page cache is the culprit - disable this, flush cache and it should work how it is required.