The story was about how the aliens had miscalculated the angles of the triangle and on a larger scale, their ships could not take the miscalculation (which became huge and ended up cracking their ship, which then crashed).
The aliens all had triangular faces and every thing was triangular.
The main idea was that pi is unresolved, which means that it could have significant impact on any spaceships that we might build in the future.
[From comment] I read it in the last two years. It's a contemporary story that I read on an online magazine (I am not sure of the name). It might have been the winner of some competition as well.
[Edit] Found it! https://clarkesworldmagazine.com/liu_09_16/