FLUSHALL and FLUSHDB commands on redis return "unk command"

Redis official Helm chart by default disables FLUSHDB and FLUSHALL commands. In this case, it is not specified in any of the redis.conf inside the containers, so you need to specify it in your Redis YAML:

master:
  disableCommands: []

It could be that your Redis configuration has renamed some commands to prevent your database from being accidentaly deleted.

Look for the following lines in your redis.conf:

rename-command FLUSHDB ""
rename-command FLUSHALL ""