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Oh wow, EFV came back to life.
Except that it goes back well before that. The decline in CTR I've experienced has been gradual but steady and goes back years...
however there seems to have been a recent very steep decline in CTR that is distinct from the long term trend.
One of the main channel cpm dropped by 50% today! I know, I know, I am Jumping to conclusion but thought I'd share my pain :)