Should I wait for more?

I could state the obvious: "Do you have a choice?"

For some things/configs, it seems to me that g can take up to six+ months to make a change. On their side it might simply be to wait and see what the site is doing, making changes, "gaming the system", or it might be that time is needed to gather reporting data (ads wise) to see where your site is going.

All of this is by algorithms, not humans, and while these programs never tire, they are also never in a hurry.

Could be other factors that are causing the CPC drop. Time of year, recession coming and advertisers pulling back, losing a major advertiser to FB, etc. It is always hard to pinpoint the reason why things go south. All you can really do is wait and see. Making changes to fix whatever might be wrong when you really don't know what it is usually just makes things worse, at least in my experience.

Thanks @tangor and @ember, based on your advice, the best thing I think I should do now is to wait without making any drastic changes.