[GGG]

Spoiler!

The fly in the problem always gets squished at the same instant at the same position regardless of where it starts.

It’s squished at the instant the two trains collide regardless of where the fly starts if the trains haven’t colides yet the fly bounces. I don’t see how the initial position changes either the distance the fly travels or the instant it gets squished

The distance travelled is Vfly*time and the time to collision is D/(Vtrain1+Vtrain2) both are independent of the flys starting position.

At the instant the fly gets squished you have no way of knowing where that fly started.

Now maybe this loss of information is described as a /0 error but my argument would be that the solution of any position is a valid solution as opposed to one driven by error.