What kind of catastrophe? Because some mangas they released on the same and other they arbitrarily chose to release 1 week, 2 weeks, 1 month later, this choice is also arbitrary. The only reason I see for that is that they want to lose money.
Saying that their choice is arbitrary doesn't make it so.
Like you know, many people that are buying just buy volumes and if they have available the digital format at the same time than the volume, than they will not even take the effort of buying either of the two version. Just reading through a 3rd party.
Or you know they turn to buying digital, but then don't like really buying it and so give up. But instead of returning to the volumes, because of the let down of the digital experience, don't even return to that.
There are many reasons why the audience would decrease giving the transition. A change of any kind normally means a decrease.
People often assume that exchange of format is simple and that the audience of one turns of that of the other. That is not close to what happens. Just like people assume that the same people that watch a season go for the 2nd and the 3rd, but obviously is not. Or the boost of further seasons, is the same as the 1st season, that is obviously totally wrong.
People are risking huge amounts of cash here, jumping of a cliff is simple not a option. And why not? Because most certainly a cruel and painful death awaits those who jump.