Many of the methods encapsulated in AssetManager are now deprecated, we are now required to handle this in a different manner. I am still struggling with this one but will post solution here once I discover one.

Could you please share how you provided access to this user to ? 

You are the first person I've seen mention that the cron expression needs to be in quartz format. I will give it a try sometime today ! 

I have been dealing with the same issue for about 4 days now, I've tried everything on the internet at this point and still cannot get the scheduler to trigger sitemap generation.

Are you positive that your page was successfully published ?