If that doesn't work, you may have a corrupted position cache.. I'm sure there is a tutorial somewhere on how to clear this, but I can't seem to find it.
I'm having the same problem. Going back to build 9879.
Say you centered the window and CTRL+X, then opened a few more of the same windows (3 File Explorer). The other two windows are offset, naturally. Then you move the windows around and resize one, then close the original window. When you close the additional windows, the saved pos & size should be retained. The next time you open File Explorer, it should be positioned and sized as it was saved by the CTRL+X, yes?
There's also the open windows in a separate space - does that come into play? (sorry, I didn't look for the exact wording - trying to get out to dinner with my wife)
There is a massive (nearly 50-page) thread here: Solved Windows 10: Folder View Settings and Desktop Icon Positions Not Saving - Page 47 - Windows 10 Forums. As one poster noted, how is it that the entire MS development team never noticed this issue?
As a solution (on page 47, linked above), Dogsled & Intrepid1 mention ShellFolderFix, available from Major Geeks: Download ShellFolderFix - MajorGeeks. I downloaded it yesterday and it's completely cured the problem for me (so far). It's a minor fiddle to 'install' (it runs almost as a stand-alone application) but it's small, simple and free - and it's effective.
Anyway, it worked for me so I thought I'd say so. (Since it's so simple, why haven't MS sorted it out yet?)