|Here's a few more thing to try.|
Try these formulas on one of the offending cells that won't allow you to apply centering
This will show the alignment of the cell.
Shows a (tick mark) ' for left, ^ for center, "" for right.
Nothing is shown for numeric entries.
This will show the type of cell protection.
1 for a locked,
0 for unlocked.
This will show the "number" format of the cell.
There is a whole list of codes it can return, but G is for General
you can look up the =CELL() function in Help to get the whole list.
See if that gives any clues as to what's going on.