Hi Matt,
It looks like you are using the same map in all of those tests. I can open many story maps from the gallery and not see any errors (although I do see messages and some warnings), so there appears to be something about your map or a layer it contains that is causing those errors.
We have heard that some developers and power user authors find the error messages helpful to know when resources aren't shared/available, and the vast majority of people reading story maps don't use their browser with dev tools open, so these messages don't have any impact on their experience.
Originally, in the first releases of Map Journal/Series, these messages didn't appear, but we ran into a tech limitation with one of the plugin libraries used in our apps when suppressing the messages so we added them back. It wasn't our preference to do that, but we haven't had any complaints about them until now, so it seems most people don't have the strong negative reaction to them that you have vocalized here.
That being said, we hear that you'd appreciate if we would handle these messages differently. We'll look into minimizing what messages get displayed in the console and will consider otherwise hiding all messages and adding a "debug" URL parameter that devs can use to turn the messages on. This URL parameter is already implemented in Story Map Crowdsource (beta), and we will look to implement it in our new apps. For example, compare the console output from these two links:
Thanks for your feedback.
Owen
Owen Evans
Lead Product Engineer | StoryMaps