I don't think his movements were outrageous in this episode (I have seen teleportation issues in other episodes though). He could have been quite close to King's Landing when he overtook Yara's fleet at the end of last episode, based on Geography. It would not have taken long to get back to King's Landing. Then, after that he sailed around Dorne to get to Casterly Rock, which is probably a 1 week trip, and there is no reason why that scene couldn't have actually been 1 week after the scene in King's Landing. It matches with getting the Lannister army to Highgarden in the same amount of time. Quick battle at Highgarden (which it was), and another week to cart the gold back to King's Landing, meeting Cersei's 2 week promise to the Iron Bank of Braavos. I don't think the timeline is an issue with Euron in this episode, they just fast forward 1 week from the King's Landing scene to the Casterly Rock scene.
I'm much more bugged by the fact that Euron built a fleet like that in about 3 months.