Powerflex 700 PI Loop Clarification

Hi,
I need some help understanding the PID loop functionality in Powerflex 700 VC. I did some trend capture on encoder speed feedback (green), PI error (red), PI speed reference output (blue). Don't mind the three troughs as they were legit downtime in the line.
I don't understand why the PI error (in red) dropped off around 2am all of a sudden with no change in feedback or the reference signal. I would assume the PI Error changing when either feedback or output changes. Any ideas?
Thanks.

sampling error in the trend or temp loss of comms? what does it look like zoomed in?

Just looked like it dropped off. The trend was running in RSLogix500. PLC is SLC5/04 communicating to Powerflex drive. All three variables are being polled by the in one message instruction. If loss of comms, wouldn't the other two drop off as well?