Dear,
There was a drastic variation in the mining difficulty, follow sections of the log:
[2018-01-24 17:01:40] tribus block 529058, diff 278.613
..... and five minutes later:
[2018-01-24 17:05:36] tribus block 529069, diff 10557.175
..... Increase 37x !!!!
I thank those who know how to explain what happened, as this discourages mining.
Alexandre.