Try resetting the column editor - changes are saved by user. To do this, log in as that user ID, open the window with the problem, and double-click on the grid title. If the column editor opens (this function is security-required), then click the Reset button. This is to ensure that the column layout didn't become corrupted.

If the user doesn't have security rights to access the column editor, then try having the SYS (system administrator user) do the same process, as SYS has an option to reset the grid for all users.