With Plot.textX, the interval option affects the y channel which is here nominal (the name column). As a result all of your y values are undefined and no text marks are being displayed. Presumably you intend the temporal d3.utcDay interval to apply to the temporal x channel instead; that will happen if you switch to Plot.textY.
(If you use Plot.text, the interval option will be ignored, which is also fine in this case because your dates are already at UTC midnight, but it’s a bit misleading since the option is ignored. Prior to Plot 0.5.0, the text mark did not support the interval option, which is why it worked previously.)