Saw non-equilateral triangular shaped craft twice, a few minutes apart, that disappeared in a bright flash.

Driving down route 29 towards route 66 I saw in the sky, very far and very high, what I thought was a plane. There were several planes in the sky but this one was a mirror for the sun. Eventually it caught the sun in such a way that there was a bright flash, and the craft was no longer visible.  There were no clouds and thus I found this perplexing.
A few minutes later, just as I passed under 66 and approached an intersection I saw it again, only this time it was flying just overhead < a few thousand feet. Once again it flew in a plane like manner until the sun caught it and there was a bright flash / glimmer, and it was gone. This time, I was certain it was a UFO as it close enough for me to determine a triangular swept wing shape.  It did not seem as if it sped off at an incredible speed, rather that it became invisible.