Martin,
This issue has existed for at least 3 years. Below is a link to my thread from March of 2019. In that post, I mention that I’d seen this problem in 2018 also.
I had this Wizard error happen while demonstrating ERPNext to a prospect. I was very embarrassed. 
Below is a link to the (still) Open Issue on GitHub, from 2016/2017.
The community is well-aware of this issue. But either:
- People don’t have time to solve…
- …or people are not capable of solving…
- … or people don’t care enough to solve.
My Suspicions
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The error is inconsistent and intermittent. Even with the exact same code base. I’ve had it happen during installation 3 times in a row. And then succeed the next 2 times immediately later.
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I strongly suspect the root cause is a Race Condition, related to the database. I believe the database is still populating tables with rows, but the Wizard doesn’t wait for that to complete.
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UOM seems a very likely candidate. So does Time Zone.
When I first encountered these issues, I couldn’t solve, because I didn’t know enough about Python and Frappe. I’m now probably capable. But over the past 3 years, I’ve become entirely fed-up with installation, Bench, and the entire setup and configuration process. So I permanently forked Bench. And have committed to writing a replacement installation tool.
In the meantime, the Setup Wizard remains unsolved. It happens to many people. They just try, try, try again. Until the stupid thing finally works.
I’m doing installations this week. Very likely I’ll encounter the same issue. If I solve it, I’ll share my code and solution somehow.