Curious, does it allow you to publish the datasource separately to 2018.2 server?
How many Mb is your extracted datasource?
Are you also using Tableau Desktop 2018.2 for this test?
I'm not sure what the problem is, I would open a case with this info.
I am in Desktop 2018.2 and I just tried to publish the datasource separately to the 2018.2 server. It is still running after an hour and I don't think this will succeed either.
My gut says it isn't a 2018.2 issue since we had the same thing with 10.5 on this test server. I thought we should compare the Windows server settings and Tableau configurations to confirm that the 2 environments are the same before I submit a ticket - but I don't know enough to know what to look at!