Walkthrough: After defeating Captain Lana's Trial within Brooklet Hill, you will be able to continue down Route 5 since you can now remove the Sudowoodo blocking the way. By doing that exact thing, the Ultra Recon Squad will appear once again, this time surprised how Sudowoodo wasn't actually a plant. They will be extremely fascinated by the Pokemon in The Alola Region, so much so that they will ask to battle you again. It is here that you will encounter your very first Ultra Beast, as their only Pokemon will be Poipole.
Ultra Recon Squad Dulse - Level 20 Poipole