Entirely possible this is seasonal. Advertisers have ever-changing budget priorities. If your channel is pulling a lot of advertisers who target back to school or end of summer sales then you would have received a bump in those months only to find that these advertisers have now depleted their budgets. On the bright side you should see an uptick in CPM's and overall revenue from November-December as advertisers dump their last remaining budgets on the holiday season... of course they will be tightening their belt once January roles around.
I actually do not target anything school related. My channel is pure tech reviews. Things like game cameras, security cameras, portable car boosters,
This may or may not be relevant but there is a general overall pullback of YT ad revenue recently.
YouTube Ad Revenue Drops 1.9% in Q3, Alphabet Misses Wall Street Expectations
A pullback in ad spending cramped YouTube's revenue for the third quarter of 2022, which declined 1.9% to $7.07 billion.variety.com