I just completed a long document designed as A4. Now I have to also convert it to US letter. Much of the document resized when I changed the sizing in document setup (file menu), but some of the master page items did not auto-"relocate" themselves. However, when I attempt to move these master page items—either on the master page, OR using an override, these elements appear locked. Even if I try to set up a new master page and apply that to the "child" master page, the incorrect item that is resisting the override, is STILL there, now creating duplicate footers on all of the pages where the original footer first appeared. SO many of the original deisgn features of InDeisgn that made it such a joy are now buggy as you attempt to "improve" this once wonderful and dependable product. PLEASE don't reinvent the wheel if you make the engine die every time you try to start the car with the shiny new hubcaps.
I am experiencing a very similar issue. I've created a very simple document where 99 of 100 pages will have the same elements, but for the first page, I need to override the master page elements. The command simply does not work.
I would like to agree with the original poster, that simple things in InDesign simply don't work now, which is very frustrating considering how much I pay for access to this program every month. Stop trying to reinvent the wheel. I want the program I used without issue 5 years ago.
I would only suggest there might be something else at play here, like an additional master page, or perhaps the item was overridden and unlinked from the master page and locked on all the individual pages.
I don't really know, just guessing.
If you can share your file I can take a look and hopefully get to the bottom of it.