There's no Gmail related settings in local.cf. We still don't know why it has score -99.525. Please try to decrease '$sa_tag_level_deflt' in Amavisd config file (for example, -1000), so that Amavisd will always insert 'X-Spam-*' headers, then we can know why new spam emails have low scores.
P.S. Please remove below lines in this file. It's configured by iRedMail by default, but it's not good. Restarting Amavisd service is required.
whitelist_from_spf *@126.com *@163.com
whitelist_from_spf *@sina.com *@sohu.com *@tom.com
whitelist_from_spf *@live.com *@hotmail.com