I upgraded from Jenkins 2.263.4 to 2.277.1 on 03/24/2021.
After this upgrade I could no longer save my matrix configuration jobs, and the tabs at the to of the page where incorrect.
Selecting Save or Apply does nothing.
The following image illustrates the problems. Notice that that the tabs are incorrect, and it's missing tabs for the Build section and the Post build operations. Moreover, there is some stuff squashed to the side of the screen under Build Triggers.