Interesting to think about the horrible ambient smell that must have existed even in these noble-class locations at the time. A wooden floor built over a giant open sewage pit.
Without reading German links, I suppose that either some architect had had a bright idea that a giant 640 KP latrine should be enough for every occupation, and thus wouldn't ever need to be scooped, or that people were mostly crushed by rubble, and the adjacent common-sized latrine also broke.
Though in some periods latrines were used to make certain chemicals, and therefore the building could be seen as what we now call a chemical plant.
[...] im oberen Stockwerk der Dompropstei des Marienstiftes zu Rat, als der alte und wohl auch morsche Boden des zweiten Geschosses plötzlich unter der außergewöhnlichen Last der vielen Menschen zusammenbrach. Dabei stürzten die meisten Anwesenden in die Tiefe, wo auch der Boden des ersten Geschosses dem plötzlichen Aufprall dieser Last nicht standhielt, sodass die Herabstürzenden noch tiefer in eine darunter liegende Abtrittgrube fielen [...] andere wurden durch nachfallende Balken und Steine erschlagen oder verletzt.
Btw, this is what this looks like today: https://de.wikipedia.org/wiki/Erfurter_Dom#/media/Datei:Erfu...
Its auxiliary buildings are long gone, and even auxiliary buildings from later centuries are long gone, too, and the church itself was converted and rebuilt many times.
The Chronicle of Reinhardsbrunn, at least, does make specific mention that the nobles fell into a cesspit (cloaca) and died miserably by suffocating in the filth (sceno suffocati miserabiliter interierunt).
To fill a floor to a depth enough to "drown" would require several years of collecting, which means it would be well decayed and much closer to soil than sewage.
But it sounds too improbable to have happened.