A CPL that's flat for six months reads as stable. It isn't — it's a market that's moved and a media plan that hasn't. Competitors are testing new creative, new audiences, new placements, and every quarter of flatness is a quarter of relative decline you don't see on the dashboard.
The fix is rarely more budget. It's usually a rebuild: new audience segmentation, a real creative testing cadence instead of the same three ads rotating since Q1, and a look at whether spend is still going to the channels that earned it two years ago.
The account that looks 'fine' is the one that needs the audit first — the one that's visibly broken already has everyone's attention.