High CPM and revenue are observable during Q4 of the year as it is a long festive season including Thanksgiving, Black Friday, Christmas, and New Year. This is when advertisers usually spend their budgets because the demand and traffic are high.
Come January, you will notice a drastic drop in CPM by as much as 50% marking the official end of the holiday season. The advertisers are not willing to pay as much for impressions by this time as most of them already exhausted their annual budget and usually allocate a minimum amount for January.
There's no need to worry, it's not your channel's or the network's fault. This is normal and common globally among all creators and publishers. And as this is only seasonal, rest assured, your CPM and revenue will make a steady comeback in the coming months.