You have created subdomain for existing domain. When you tried to switch off DNS service for created subdomain, the following message was displayed:
The DNS records of this subdomain are stored in the parent DNS zone. You can modify the parent zone here or create a separate zone for the subdomain.
When you have checked DNS records of main domain you found that DNS records for subdomain was not created.
The issue is considered to be a software issue #TP-144515 and will be fixed in future product updates.
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