As Homepin said, they weaken from heating up and cooling down, I normally replace a fuse once as a test and then fault find if it blows.
It's strange that fuses would start blowing in different machines at the same time (over a week or so).
Only common thing that comes to mind is check the power point voltage (240V +- 12 volts), it may have changed. Power companies raise or lower voltage tapings to an area sometimes.
