I was following the guide on this page to try to set up Dual Tagging. Looking at a GA debugger in chrome I can see both UA and GA4 events being fired.
However, it looks like on releasing the code to do this, many UA events are not making it into GA (not all but a significant number) and some events seem to not make it at all. I can't see an apparent reason for this. I'll need to do more debugging to see where the events are going but it also seemed worth asking here in case there are any known pitfalls of doing this.