Actually if you zoom into the 5th photo, you can make out something in white which I think is meant to depict/give an impression/represent a corpus .
I too was thinking of Passiontide as some places veil in Red instead of Purple. And the Rite of Ordination to the Diaconate, I guess would explain the white chasubles (though red = Holy Spirit, may also have been used, but perhaps they didn’t have enough red chasubles for all con-celebrating priests). But as there is also red flowers… perhaps they were permitted just for this rite, or if it was The Mass of the Lords Supper, perhaps??? Though for that particular Mass, I would have thought white flowers, but maybe red to signify the Holy Spirit for the Ordination??