Maybe they have fixed it in the meantime, but upgrading the core Magento 2 failed with a lot of errors, when making use of Redis cache. Which, I must say, is a performance booster.
So, to prevent that, before upgrading the Magento 2 core, type in:
redis-cli FLUSHALL
on the command line before upgrading and deploying static content. That’ll save you being smacked with a lot of errors.
More about Redis and Magento 2 here:
https://devdocs.magento.com/guides/v2.2/config-guide/redis/redis-pg-cache.html
