The OP first asked what the origins of "dogmatic sedevacantism" are. It was just TKGS and I who addressed that correctly.
Then the OP asked if there is anything from approved Catholic sources forbidding us to be "dogmatic". Everyone seems to have gone off on tangents with merely their opinions about sedevacantism, and not the descriptor "dogmatic".
A dogma is a solemnly taught doctrine. So, nobody professes that sedevacantism is a dogma, obviously.
However, a dogmatic fact is a fact that has a direct bearing on a dogma. For example, if an archaeologist ever claims to have found a bone of the Blessed Virgin Mary, we have the duty to say it is a dogmatic fact that it is not. We don't have to wait for the Church to decide that.
The Church says it is our duty to be dogmatic and to proclaim with certainty what we know to be a danger to dogma. Read the second-to-last chapter of "Liberalism is a Sin", it's all there, and praised by the Holy Office. It condemns the idea that we should wait for Rome to decide. Very easy to google on-line.
Someone mentioned about most sedevacantists being emotional. Is there something wrong with being emotional? No, there isn't, unless that emotion makes no good sense along with it. The greatest of preachers of old appealed to emotion, and it was good when accompanied by good sense and good doctrine.
How about the good sense of someone without a lot of learning but with a strong faith? Is that just pure emotion? No. If a 60 year-old grandmother says that these men promoting Vatican II cannot be true popes, because true popes cannot be behind such erosion, that is not emotion, that is a strong virtue of divine Faith. That woman can only pray for those with weak faith who think that a pope can be head of the true Church and head of a false Church...as the SSPX had expressed. I have yet to see the Resistance condemn such nonsense.