Due to the use of hard beaters, xylophones are prone to face and edge damage.
Whilst it is easy to see the wood splintering at the edges, damage to the face is harder to see, but both will reduce resonance, and of course affect the tuning.
Vibrations don’t only travel along the length of a note bar, but also across the width and through the depth. The grain of the wood runs up the length of the bar. Below is an example of the cellular structure of hardwood:
In general the cells are lying like long strings of sausages alongside each other, stuck together with cellulite. Vibrations go along the length very easily, but meet more resistance going across the strings of cells. A crack creates a void that the vibrations cannot cross. So depending on where the crack is will determine whether anything can be done.
Glueing the pieces back together is not practical, but also will not solve the problem. A crack through the entire depth of the note means a new note, any repair will be temporary – the wood will always be trying to get to a relaxed state, glueing and clamping is stressing it.
So the only option is to remove any loose wood that is dampening the sound. As it is removed, the improvement in resonance can be clearly heard. It looks drastic, but the note is useless as it was, and repair is cheaper than making a new note.
The photo shows that the left hand edge has been cleaned up, but the note still didn’t sound, so the face was examined, and a crack discovered. That groove in the face is about 3mm deep.