When using a digital trigger with the PXIe-5172, there's a delay between when the trigger is received and when the data is acquired. This signal delay is caused by the longer signal path for the incoming signal. The trigger pulse travels a much short path through the module, causing the module to start acquiring before the signal of interest has made it to the ADC. Using the trigger delay property node will delay the digital trigger to account for this signal path.
It is important to acknowledge that this delay varies and has a minimum time of around 600ns and it is something expected for the PXIe-5172, so it is naturally not an error from the hardware but a condition to tune up with a trigger delay if an application can't withstand a delay on the order of nanoseconds.