When nodeSize is 1, nodeRank is always 0. Therefore, if there are no heads,

nodeFlag becomes always 0 and so, the temporal directory where the checkpoints
are being stored is not renamed and then, in the restart, FTI is not able to
find the checkpoints, although they exist, because they are not in the expected
directory.
Changing the condition "nodeRank==1" to "nodeRank==0" when setting nodeFlag,
this issue is solved and the checkpoint/restart works as expected.