It’s quite possible that GTM (Google Tag Manager) and the hardcoded GA4 tag are interfering with each other. As such, you might have to consider consolidating your setup around a single implementation. In your case, it’s advisable to move the hardcoded GA4 tag into GTM as GTM can natively handle GA4 tags. For your custom events, instead of using gtag('event',...) in your code, you will need to make use of GTM’s event tag setup. You can continue triggering certain events in your single page application via Javascript. Ensure to use dataLayer.push to push the events into data layer and then instruct GTM to listen for that using the Custom Event trigger. It might initially seem a bit more work, but it will help debug issues in the future and provide a centralized platform for managing your all of your tags along with the custom events you need.