Inaccurate water volume is caused by air bubbles trapped in the system.
Perform a manual backflush immediately. Press and hold the banana-shaped water volume button and the round water-making button together for 1 minute. This will purge the air.
If the problem continues, ensure the glass carafe is properly positioned with its cover closed and connected to the system. An improper seal can affect volume measurement.
Also, note that during the first two rounds after changing filters or refilling, the raw water fills the filters and little to no clean water is produced. This is normal. The selected volume (0.5L,137 1L, 1.7L) is the target output; actual output can vary slightly based on input water pressure and temperature.