As a developer, it is currently impossible to work with SetCore when your game is loading. You never know when the parameters are going to be set up, and they just leave an error. This causes developers to have to work around the issue by repeatedly setting the values until Roblox finally allows it. Ideally, these errors should never happen for valid SetCore parameters (such as TopbarEnabled, ResetBindableCallback, etc).
This is an issue that has been around for years, when I was writing this post, this is the list of suggested topics Discourse gave to me.
