As you say, weird.
The image is just a jpg exported from LR.
I can't think what EXIF data element is throwing things out, or even how to correct this.
BTW it wasn't just that image. As you may have spotted I tried to post another image a few days ago. I had the same trouble with that one as well, but it cleared and the image posted.
As you say, if it happens again, I'll flag it.