When editing event details, the WordPress editor toolbar dropdowns such as heading selection & color selection stop working when the event details are scrolled to the point where the toolbar converts to sticky.
EE version 5.0.10.p
I’m not getting this on any of my test sites, so if you test this with just Event Espresso and the WP User integration enabled do you get the same problem?
Tools -> Site Health -> Troubleshooting -> Enabled Troubleshooting mode.
That will disable all plugins and switch to a default theme and then allow you to enable specific plugins whilst in troubleshooting mode. Once disabled you will revert back to the current state.
May we also the theme you’re using? you can also test the theme if there’s possible conflict. you can also use that plugin to check this.