I think Unity had some security issues recently that created vulnerabilities for many game developers which gave them no choice but to update their game to a newer and more secure build.
Viewing post in Unity vulnerability patch comments
Yeah should have been pretty simple to fix, think they just had to recompile everything on the fixed version of Unity. Still annoying for devs to have to deal with it and theoretically possible they could have needed to fix a few things if something on the new version of Unity caused any bugs. There was also a way to fix the old version, if needed I believe. Not sure you care but that was my understanding - if you are curious Unity's website has all the details on the issue but it is kind of technical.