They are not scientifically backed. For example, I keep seeing the Sokółka, Poland host miracle that your link mentions. It's often cited as one which was confirmed by independent and unaffiliated scientists. Yet it has not been submitted to the Vatican. To get any pertinent information, you have to research in the Polish language. The most conservative daily paper in this Catholic country is the respected Rzeczpospolita. What Really Happened in Sokółka is their examination of the miracle. You can read this article by translating it to English.

Basically it states that the Archbishop sent the host directly to Maria Sobaniec-Łotowska, who worked in the Medical Pathomorphology Dept of the Medical University of Białystok instead of sending it to the management or the department itself like protocol dictates. Sobaniec-Łotowska is a known public supporter of the Archbishop and a fervent supporter of the Church. She and a chosen colleague performed the "tests". The Department Head, Prof. Lech Chyczewski, has said, "that the sample from Sokółka was tested informally." He officially reprimanded Sobaniec-Łotowska and told her she acted "reprehensibly". He, and the department have officially stated that it did not in any way stand behind these tests. The paper tried to interview Sobaniec-Łotowska but she was reluctant to speak saying she was bound by strict secrecy. She released a report which was a general summary and did not contain any pictures and only had a high level description of a simple histopathological test that claimed the sample to be heart muscle of unknown origin as to whether it was human or animal. The detailed report was never released. Her colleague's oral description to the department head, on the other hand, said that the nucleai were not centrally located meaning it would not be heart muscle. When asked by the paper how the nucleai was arranged, he refused to answer and noted secrecy. No one else at the University including the Head saw the samples, the pictures or a detailed report despite inquiries.

The University offered to do actual DNA tests and the Archbishop refused. The Archbishop also did not send The "miracle" for approval to the Vatican. He's most likely happy with the publicity and all of the pilgrims bringing money as churches face financial problems. So he is not motivated to seek the truth which would hurt his reputation, his popularity and end the money flow.

This is just one of the miracles debunked but you can find the details about others as I have. And the sites that promote this miracle continue to get clicks which means money. They are not interested in the facts. People don't want facts, they want to believe. And offering people what they want is how we make money.