Reported by @magarzon in the #support channel of Symfony's Slack:

Is there a way to disable the cache for the serializer? I'm having problems with the cached metadata, I've tried to set cache: false in framework config, but it's not working

Weird thing is that there is a service defined serializer.mapping.cache.symfony that is a "memory cache", but that doesn't works with the serializer, it complains that doesn't implements Doctrine\Common\Cache\Cache interface. Probably an issue?

because it has the "same" name as the recommended cache in the documentation, serializer.mapping.cache.apc

Probably it's my code, I'm going to check

No, it's not my code, it's documentation not up-to-date and probably bad naming: serializer.mapping.cache.apc is deprecated since 3.1, but is still recommended in this doc without any warning: https://symfony.com/doc/current/serializer.html#enabling-the-metadata-cache