Designing concert halls has always been a tricky business. To get the “right” sound engineers try to get a good balance of reflection and absorption. Too much reflection results in an empty, hollow sound. Too much absorption deadens the music.
The concert hall may have stayed the same, but its audience had changed. Most importantly, women were no longer wearing the billowing, layered sound-absorbing gowns that had been popular earlier. The new styles were shorter and simpler, and didn’t absorb sound as well. Overall they changed the balance of reflection and absorption of the sound in the room.