Running drush cc all -y generates errors

[Wylbur]

The following error appears in the watchdog log when running drush cc all -y

The function drush_cache_clear_both() (cache.inc:99) called deprecated function drupal_flush_all_caches(). It will be removed in the next major release of Backdrop.

Drush version : 8.4.9-dev
Backdrop Drush : 1.x-1.x

[herbdool]

It looks like not so much an error as a warning. Clearing cache still works I'm guessing? Not sure how easy it is to replace it with the Backdrop version, but until then can ignore the warning.

[Wylbur]

This was my issue, had an old version of drush installed.