Wish I’d had a camera at the time but a cartoon will have to suffice, representing two actual incomplete rainbows that stop in midair where they meet, lit only by a setting sun.
This seemed so paradoxical, I honestly wondered if it was a dream. After all, on a normal rainbow with two arches, the arcs do not touch and the larger one is very much fainter with a reversed spectrum. The arches schematized here were indeed accompanied by typically-faint concentric larger arcs that also stopped abruptly where they, too, met, exactly above the main meeting point.
Being awake, as it turned out, I discovered the simple explanation for this, related to an often-subtle and less dramatic everyday phenomenon that is readily understandable in nonscientific terms. I had enough information at the time to solve this like a puzzle, though, and now you do too.
What was that simple explanation for this odd pair of rainbows?
Notes. Only air was between the point of view and these rainbows. The less complete rainbow, to the right, is slightly brighter and both arches brighten the air directly below them. The picture has been revised to more clearly represent how the rainbows end at slightly different places, muddled by their overlap.   The larger arch ends a little to left (and slightly up) from where the smaller arch ends.   The rainbows were not as thick as depicted (none are) and had further characteristic features that scientific photography would reveal to extend a vertical pattern of similar meeting points.   Safe to guess that this effect was not observed by humans more than a century or two ago, although tiny animals may have experienced it over the course of eons.   Some details of the real-life story have been altered in an attempt to stymie internet searches.
Here is an added diagram meant to emphasize that the position of a rainbow depends on the direction of incoming sunlight and that the size and distance of any rainbow are intrinsically ambiguous because the mist that creates a rainbow is rarely at a single distance and the resulting image occupies the same portion of the visual field regardless of actual distances to individual mist droplets. More information can be found all over the internet, such as Wikipedia and (less laboriously) earthsky.org.