The phrase "unfortunate coincidence" means that two events or situations happen at the same time, but it is unfortunate or unlucky because they have a negative or undesirable outcome. Full definition
So it's a really unfortunate coincidence for first lady of the United States Melania Trump that Tuesday was the same day news broke that she is apparently working to... (gizmodo.com)
In Hollywood fashion, the Bruins gave Mora the pink slip on his 56th birthday in what can only be termed as a really unfortunate coincidence. (sbnation.com)
The BBC did not discipline him and called the license panel «a very unfortunate coincidence.» (businessinsider.com)