You can get the official S5P NO2 products from the S5P Hub or new dataspace service. This is the only official source for this data and this is where you should get it.
Apparently KNMI also distributes the NO2 data via their TEMIS website, but in a reduced form (which is why the files have a ‘reduced’ postfix in the filename). This apparently removed variables that HARP is expecting to find, such as the satellite altitude. I will contact TEMIS/KNMI to ask why they are providing reduced data in this form, since it is hurting usability.