The problem kept occurring… after digging deeper I found that only uninstalling Homebrew and then re-installing it solved this issue.
Uninstalling will remove all your brew packages, you can save the output of brew list in a file first, to have a record of what packages were installed.
Uninstall Homebrew:
/usr/bin/ruby -e “$(curl -fsSL https://raw.githubusercontent.com/Homebrew/install/master/uninstall)”
Then re-install it:
/usr/bin/ruby -e “$(curl -fsSL https://raw.githubusercontent.com/Homebrew/install/master/install)”
Unfortunately you can no longer chown /usr/local in High Sierra. A workaround is to sudo mkdir /usr/local/include and /usr/local/Frameworks if they don’t exist, and
sudo chown -R $(whoami) $(brew –prefix)/*
Thanks to ilovezfs for this simple workaround and for the amazing homebrew!