this mondolin is build with a solid top wood [sprus].the couse for the split at the center joint is the shrinking of the wood.
remember,this is not a crack.aiging is a hardening [shrinking ] of the mikrocels of the wood.when this hapens the wood loosses its flexibility and cracks ezy when expoused to chenging umidity levels.the proper way to fix this mandlin is by insrting strip of aiged sprus wood.this is a job for expert luthier.