Did GA4 kill my UA events?

[Pspec]

Hi all,

I'm working with a client who's just made the switch to GA4 - it was a simple setup, using the GA4 setup tool and using their existing onsite gtag to create a new property. We've noticed that the custom events they had set-up (coded into the site, not done with GTM) have seen a massive dip since the installation when checking the UA property, even though nothing else was touched.

All other traffic and the goals pulled through without any issue and are still showing normally, but these custom events have seen a real dip. I've checked onsite, their GTM, anything else that might explain it and come up empty, and the timing seems too convenient for it to be anything other than for it to be related to the setting up GA4.

Any other suggestions or pointers for anything I might have missed are greatly received!