Have a 23hp Kohler Command engine that was behaving similar to yours. Run fine for about 10 minutes, then started losing power. Replaced both coils and issue disappeared. Was pretty sure that 1 coil was going dead after it warmed up.
But on top of that, the mags are super rusty and the gap is crazy inconstant. That’s not supposed to be off that much on the second part of the coil, is it?