tnag

The second from the last picture is 'ringing'.  it is most often caused by a bad ground somewhere.
There is something amiss with your Pi Zero2W. You stated previously, you have 2 different models of Raspberry Pi computers, one shows the problem the other does not.  If the same problem was seen on both Pi's I would say the issue is the MCC 172, but since it does not. I have to conclude it is the Pi Zero2W, and  recommend you contact the vendor of the Raspberry Pi Zero2W.
Regards,
Jeffrey

Hello Tatsuro,
The onboard micro on the 172 handles the SPI communications to the ADC and buffers the data, so it is not affected by the Pi processor load.  As long as you don’t get overruns the data should be considered valid.  Do you see the same spikes if you measure something without IEPE?
I posed your issue to one of our hardware engineers.  After reviewing the schematic of the Raspberry Pi Zero2W, here is his response
The MCC 172 is powered by 5V passed directly from the micro-USB connector, but due to its small size there is not much room for capacitors on 5V.  You may have better luck if you find a way to add additional capacitance to the 5V net right at the Raspberry Pi (between the GPIO header 5V and GND pins would be a good location.)  Pi CPU activity may be causing supply spikes.  I suspect more bulk capacitance would help (47uF – 100uF), but you would need to experiment with different values.
Regards,
Jeffrey

Hello @tnag
Based on the information you provided above, You have proven the MCC 172 performs admirably when operated with the Raspberry Pi 3B.  The noise occurs when you use the Raspberry Pi zero 2W. 
Meaning the problem is not the MCC 172.  Suggestions:
Try a different RPi Zero 2W;
Try a different power supply than the one you used with the RPi Zero 2W or check it's output for noise;
Contact the vendor of the Raspberry Pi Zero 2W and provide them you test results.
Regards,
Jeffrey