When the developers of a game do not include a change to the game in the changelogs, usually to "nerf" or decrease the effectiveness of an ingame mechanic or item. This is done to avoid angering the community, but generally ends up doing the opposite.
The devs silent nerfed the pyro, how am I meant to play now?
When game developers nerf a game aspect/character and don't announce it or include the change in any patch notes.
Did the new character get a shadow nerf? His fire rate feels much slower than it did before the new update, but I don't see any changes to him in the patch notes.