The big core algo update might have had something to do with how brand keywords impact sites that are not the brand. You can find the story at The SEM Post, where they write:
"There were definitely signs that these changes were quality related in some way. But one analysis seems to be pointing to the fact that it is related to brand keywords and how websites that are NOT the brand are ranked for them."
The SEM Post story is about analysis from an SEO named Bartosz Goralewicz, which you can find here: https://goralewicz.com/blog/googles-new-brand-bidding-algorithm/