CompactLogix 1769-IQ16 input status

I have a problem with a CompactLogix 1769-IQ16 input card. The card is being used in sink mode, the OUTPUTS of the device connected to the card switch to zero (open collector output, NPN). The problem is that even though the LED's on the front of the input card are lit, the status of the inputs when monitored online momentarily go to zero every now and then.
I have measured the voltage between the input terminal and ground when the input is supposed to be on and it is sat at 0.53v. This looks correct to me. Any body have any ideas?

Well Pauly, i think its just the Read Gap / Delay in Monitoring.
Are you monitoring it on PG ?

Using a laptop yes

I'm using a laptop. The status on the HMI that is looking at the same bits is changing as well. Eventhough the LED's are solid on on the front of the card as I said