The fuck up for me wasn't the performance of the border guards who as you pointed out seemed to have performed as needed given the intended Blitz to the Kursk NPP was slowed enough to give the Russian forces time to organize and halt the progress of the Ukrainian special forces. For me the fuck up was Russian intelligence not catching the build up of special forces on their border in such quantity with all the vehicles and supplies they would end up assaulting with. On the other side, the Ukrainian military was somehow able to hide this operation from the Russians and executed their mission about as well as anybody could've realistically expected. Apparently the military leadership in Ukraine thought is was a foolish thing to try to do and clearly wasn't successful in accomplishing what Zelensky wanted.

Sorry for the crazy late reply.