I think it is a bug in the core src and it is related to the timestamps that I believe roll over after 71 minutes which is coincidental to the time that the mesh break apart broke apart.
The timestamps seem to influence the prominence a device gets in the mesh like becoming the master or the slave. EasyMesh has the goal of being self configurable so depending on exactly when a device joins sets its prominence.
I have a UDP network but is has fixed prominence in that each device has a designated roll. EasyMesh represents a good alternative and can survive a device going offline.