Unfolded Circle rename page on R3 is not possible see video link:

[SunBeech]

Check my earlier post and temporary work-around:

Cannot rename some User Interface pages (BUG & BYPASS)

I assume this is a user interface page in the activity. If so, is the grid size larger than the default 4x6 and you placed one or more button(s) in the larger part of the grid? Then you are running into this issue, for which I created a bug report: You need to (temporarily) move those extra buttons to another page and change the page’s grid size back to the default size. Then you can rename the page. After that you can change back the grid size and re-add the extra buttons.