This is an Upgrade from 2009 to BC 14 (on premise) by way of NAV 2015.
Upgrade step UpdateItem failed with error: "Table Product Group (5723) is obsoleted ..."
Isn't this the job of the data upgrade to transform the data stored there to "first level children of Item Categories" as stated as reason for obsoleting the table Product Group. Indeed, that was, what the code would do, if it not stopped on this unreasonable error.
Strangely, the upgrade process did not stop on this error, even though I run it with option -FunctionExecutionMode Serial
I performed an update from NAV 2016 to the same version of BC before, and did not encounter this problem.
What causes the failure, how can I prevent it, and how do I convert the Product Groups to Item Categories now?