In recent years before Pesach a number of singers would get together and have a nice evening of music for yeshiva bochurim.

Sounds like good, kosher, fun. No women allowed, all kosher music, kosher singers. Shouldn't be a problem.

This year it was set to take place on the 10th of Nissan, April 18, and to include Mordechai Ben David, among others.

Shortly after it was announced the event was already canceled.

Mottka Bloi, the head of the Guardians of holiness and education, or whatever they call themselves, announced shortly after the initial announcement that the event has been canceled, as the event is against the wishes of the gedolim, as they disapprove of all such types of events.

It is canceled for now, at least in its current format. Maybe it will be changed and get put back on the table, or maybe not.

It seems the problem with it is that this event is being advertised as an erev shira and not a kumzitz. It seems erev shira is problematic (though I dont know why), whereas a kumzitz would have been acceptable.

As well, Mordechai Ben David refused to sign a commitment that he would not appear in other events that did not receive the approval of the gedolim.
source: Kikar

Seemingly good kosher fun, but some people did not have authority over it and could not get the participants to grant them control, so they had it canceled. I don't know what is different about what was supposed to happen this year than what happened in previous years, or if it is just a matter of this time they were successful in thwarting the program.

The holiness and education people should just not be surprised when the bochurim who are bored during vacation and looking for interesting things to do find things that are slightly, or not so slightly, less kosher to do.