until recently, my JabRef was always able to retrieve bibliographical information about books and articles by DOI. These last days, it did not work anymore. I first thought it was a problem with the specific DOIs I provided (in that there is no inforrmation about them in the database), but I got suspicious and I have now seen that even for entries I am completely sure I created using the DOI-based information, JabRef cannot obtain any info anymore.
What could be a reason for this behaviour? I am running JabRef 3.8.2 on Win 10.