Problem
In certain circumstances, you might still see the following error "Migration failed: Subsite could not be created" when trying to create a subsite.
This can be caused when CloudM Migrate believes that the Parent site does not exist so the subsite cannot be created.
Solution
When migrating to Microsoft 365, navigate to the Destination Settings screen, select Advanced Settings and set the Provision Sites Timeout Check setting from the default 180000ms to a recommended 300000ms (3 mins to 5 mins)
Continue the migration process as usual.