60% loss is way too high
I'd check the basics first - what traffic source are you using, are there multiple redirects, is the tracker firing correctly, and are you comparing clicks to real page views or to GA4 sessions?
I've seen cases where the network counted every click, but a huge chunk never actually loaded the page because of accidental clicks, bot traffic or poor mobile connections
If you're buying push or pop traffic, 20-30% loss can happen. 60% usually means something is broken or the traffic quality is terrible