Recording to this Update on feedback@checkmk.com post I will just post the “problem” here. Its only a cosmetic btw, it finished before the time it estimated.
This hit my eyes when I renamed one host:
And I think it was a bit too generous 
In fairness, the inline help warns you that…
The renaming of hosts is a complex operation since a host’s name is being used as a unique key in various places
I didn’t know it was that complex though 
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