Ran into the same issue with the new 2021 version: Correct response variable not recognised for new experiment with new version: 'key_resp.corr' always FALSE - #15 by TParsons.
The problem seems to have been corrected-just undocumented as a correction–in the latest version. It took me some wrangling to get the new 2021 version to recognise the experiment I wrote in the first 2021 version (i.e., to update the “last run” python file), but it you play around with the version settings, you can eventually get it working. How, I can’t say, but if you mix it up and experiment enough, it’ll work.