Error: "Unable to JIT the user"

After logging in to Google we see an error response from Okta:


Investigating the Okta log we see:

ErrorMessagewith the following validation errors: identityid field failed validation with value ‘null’: Value for required property {0} is missing.

Could you assist us here please?

we have created a mapping from email to that field now – but why is it required suddenly? we still have old users with an empty field – yet new ones must be given a value for identityid. Why?

PS we are on