This usually means the unit is not regenerating properly rather than the water changing.

A softener only works if it draws brine through the resin on schedule. A salt bridge, an empty tank, a bypass left open, or a setting wound to the wrong hardness all end the same way, with untreated water going to the house.

Look for a crust you can push a broom handle through in the salt tank, salt that has not dropped in months, a bypass lever turned sideways, and scale coming back on the kettle and the shower head.

Do not buy a new softener before someone checks the salt bridge, the bypass, and the setting. All three are free to look at and any of them will stop soft water on a unit that is otherwise fine.