Please see the forum link above for all the specifics, but the crux of it is that in the original version of Catchup, you could claim a hexagon creating a group up to the largest group on the board without triggering the catchup mechanic. But with this new rules change, even tying with your opponent now triggers an extra claim for them on their following turn.
I’m working on an update to Catchup to make it iOS 11 friendly, and support the new iPhone X screen size, and figured while I’m at it, I’ll add this new rule as an option in the app. So I’ve created a new toggle in the game options, and I’m leaving it off by default, because I don’t think most people will know about it, and I don’t want it to take anyone by surprise. Also, for now, because I don’t really know how I would indicate which version is being played in the UI, you won’t be able to play with the new rule in online games. If there is enough (any?) clamber for it in online play, I may consider adding that in the future.