Got warning: 'WARNING [cache] Failed to save key' after update doctrine configuration

I got a warning: 'WARNING [cache] Failed to save key', after trying to update the doctrine configuration. this error appears when i run bin/console.

I tried updating the doctrine configuration to get rid of the deprecation warning I got.Previously my doctrine configuration was like this:

orm:    entity_managers:        default:            metadata_cache_driver: apcu

with this configuration there are no errors or warnings that I get. there is only a deprecation notice.then I try to update the configuration to be like this:

orm:    entity_managers:        default:            metadata_cache_driver:                type: pool                pool: doctrine.apcu_cache_poolframework:    cache:      pools:            doctrine.apcu_cache_pool:                adapter: cache.adapter.apcu

and i got 'WARNING [cache] Failed to save key' when try run bin/console.

I know the problem is because I haven't enabled apc.enabled_cli in my php.ini.but what I'm asking is why in my initial configuration the warning didn't appear even though apc.enabled_cli = 0

Thank you !