Hi there,
Swiss pension funds are only legally obligated to pay you a pension based on compulsory contributions. If you make voluntary contributions to close gaps in your pension savings (when you get a raise, for example), that voluntary portion of your pension savings does not fall under the same obligation.
While most pension funds pay a pension based on your total contributions - both compulsory and voluntary - they may in some cases choose to use just part of your voluntary savings for your pension, or none at all. When your pension is not based on voluntary savings, those voluntary savings may need to be cashed out as a lump sum.
Best regards from Moneyguru