Hi there,
Deficits in Swiss pillar 2 pension funds occur when the fund no longer holds enough assets to cover pensions and benefits. Deficits may be temporary if they are caused by simple fluctuations in the value of investments. But they may also be ongoing if the pension fund makes a loss.
When pension funds make a loss, they are allowed to stop paying interest on voluntary contributions (not compulsory contributions) until they regain solvency. A further measure to regain solvency is charging their members additional fees. If those measures fail to fill the deficit, pension funds may reduce the interest rate for compulsory contributions to as far as 0.5% below the minimum interest rate stipulated by law.
Best regards from Moneyguru