The short answer
Cut it four ways before you form a theory: by lead source, by segment or deal size, by rep, and by competitor present or not. One of those cuts almost always explains most of the drop, and the answer changes what you do completely. A drop concentrated in one source is a lead quality problem, in one segment is a positioning or pricing problem, in one or two reps is a coaching problem, and across the board with more competitors named is a market problem. Gong's call data adds a useful nuance here: deals where a competitor comes up early actually close at a higher rate, while competitors appearing late correlate with lower win rates and smaller deals, which usually means the rep discounted to survive a fight they did not see coming.