In some online databases such as DBLP some journals or conferences appear that are canceled or not appear at all after a few years. For what I know that is because, according to DBLP, the mentioned conference does not uphold with some criteria of quality to continue to appear on that database.
In Scimago, I have seen that a journal appeared indexed until 2016, but now it appears a message saying "Cancelled", what does it mean apart of the obviousness of that message? maybe that the journal has become a predatory one? or that it quality has decreased?