According to a source within the Democratic National Committee, the party expects to nominate for president and vice-president in advance of the Chicago August convention, even though there is no longer any publicly revealed reason to do so. As already noted, Ohio altered the deadline on Sunday, June 2, so there is no longer any problem with certification deadlines.
Nothing on the Democratic Party’s national website mentions this, and no news story I have found explains why the party is doing this. Some speculate that the party is afraid of protests at the Chicago convention, so if the party has already nominated with a virtual roll-call, perhaps that might make the convention venue less appealing as a protest zone.