In the main menus/toolbars, go to Folder > Folder Format and check what the column widths are set to there. They're probably set to auto-size.
Changes there may need to be saved for the folder, unless automatic formats are on. If you want to save a change for all folders, click the Save button at the bottom left (was at the top in Opus 12), and choose the appropriate options there. More detail here: Folder Formats: Quick Guide