If irrigation has been entered for a month, but is not showing any mm applied (shown on the screen shot below) this will be because the model does not require irrigation application to achieve soil moisture targets based on the underlying long-term climate data.
With the irrigation strategy “Trigger point and depth applied to achieve target” if the block has already got the required soil moisture from the climate data in a month then an irrigation event is not triggered - therefore not applied. This doesn't have to line up with what actually happened that month in a particular year - because it is based on the long-term climate data. It is mirroring the practice that irrigation was only applied as needed.
If irrigation is applied based on set timing or a set amount of water applied, then a different irrigation strategy needs to be entered.