Solution:

If the ADAM-4018M is set to event log mode and all 8 channels are enabled, the module will begin to scan data from CH0 to CH7. When CH0 data is compared to the high/low limit and find this value is outside the range, the data and the time would be recorded into memory. If the module is scanning data from CH0 and the input value of CH1 is outside the alarm limit range, this event of the CH1 will not be recorded. Therefore some alarm events could be lost.