Budgeting & Bidding
Ad fatigue is the most common cause: the same people in your target area have seen the same creative enough times that they stop responding to it, and Meta has to reach further (more expensive) audiences to keep delivering. This usually shows up as a slow climb over 2–4 weeks rather than a sudden spike, and the fix is simply a fresh creative — a new photo or a rewritten headline resets it.
A sudden, sharp jump is more often about competition or seasonality — more businesses bidding for the same local audience (common right before a busy season like storm damage in summer), which pushes everyone's costs up at once regardless of what you changed. There's not much to do here except widen your targeting radius slightly to reach a less-contested pool.
Less commonly, a budget increase itself can temporarily spike cost per lead, since Meta briefly re-learns delivery at the new spend level. If you raised your budget in the last 2–3 days, give it a few more days before concluding the campaign has actually gotten worse.