Recently in the past several days, when I have tried to open the Hulu app it will display the title screen and then close completely back to Roku TV main menu. I have tried to delete the app and start it again, and that didn't work. I cannot access any aspect of the app, it just kicks me back out to the Roku TV main menu.
I would try settings>system>power>system restart. Especially if "fast tv start" is enabled in that same menu. The Hulu app could have been updated, and something stuck in memory. System restart won't lose your settings like a factory reset. But, if that doesn't work, you might have to try a factory reset (in the system>advanced menu).
"People are often amazed at how much we’ve done with the number of engineers we’ve got." (Roku CEO Anthony Wood, Austin Statesman, Oct 4, 2019). "Amazed" is one way of putting it.