For anyone interested... Derek quotes 5 theorised causes but rules all but 2 insignificant, leaving the primary confounding problems as:
1. Warm liquid changing the nature of the freezer (Derek mentions melting frost into a conducting layer but there's also warm water triggering the thermostat of a freezer to work harder)
2. Supercooling can prevent ice forming in calm water, even when the water is below freezing (the effect is wildly unpredictable leading to experimental problems)
Derek then quotes the following study and meta analysis from 2016 that carefully accounts for these and other problems, which finds no evidence of the effect and concludes the other studies' claimed effects are within their own margins of error (including issues like placing thermometers at slightly different locations in a vessel giving dramatically different timing results):
1. Warm liquid changing the nature of the freezer (Derek mentions melting frost into a conducting layer but there's also warm water triggering the thermostat of a freezer to work harder)
2. Supercooling can prevent ice forming in calm water, even when the water is below freezing (the effect is wildly unpredictable leading to experimental problems)
Derek then quotes the following study and meta analysis from 2016 that carefully accounts for these and other problems, which finds no evidence of the effect and concludes the other studies' claimed effects are within their own margins of error (including issues like placing thermometers at slightly different locations in a vessel giving dramatically different timing results):
https://www.nature.com/articles/srep37665