1.8V is too low for the ChipWhisperer to properly read. It’s very unlikely that you’ve damaged anything, but I recommend using a level shifter to bring the signal up to 3.3V.
If you’ve got a ChipWhisperer-Lite, you do have the ability to set the IO voltage of the FPGA as described here: CW1173 ChipWhisperer-Lite - NewAE Hardware Product Documentation. As that section states, you do that at your own risk, as only the FPGA IO voltage is affected, so it’s possible to damage IO pins if you feed in too low or too high of a voltage.