Ionic3 GET results in

I run into a strange issue.
I have a web service with 4 operations. Two of these operations succeed and two of them fail with a 401 (Unauthorized) or 405(Method Not Allowed).
All endpoint are in the same domain

GET plus.dnb.com/v1/search/typeahead
works fine

GET plus.dnb.com/v1/match/cleanseMatch
Failed to load resource: the server responded with a status of 401 (Unauthorized)
(index):1 Failed to load https://plus.dnb.com/v1/match/cleanseMatch?name=Klm&countryISOAlpha2Code=NL: Response to preflight request doesn't pass access control check: No 'Access-Control-Allow-Origin' header is present on the requested resource. Origin 'http://localhost:8080' is therefore not allowed access. The response had HTTP status code 401.

Both GET requests get exactly the same HTTP Headers
Why are both requests not consistenly showing the same behaviour ?

The same problem is also experienced with POST request:

POST https://plus.dnb.com/v1/search/criteria
works fine

POST plus.dnb.com/v2/token
OPTIONS plus.dnb.com/v2/token 405 (Method Not Allowed)
Failed to load https://plus.dnb.com/v2/token: Response to preflight request doesn't pass access control check: No 'Access-Control-Allow-Origin' header is present on the requested resource. Origin 'http://localhost:8080' is therefore not allowed access. The response had HTTP status code 405.

If this is a CORS related issue, then why is the behaviour not consistent ?

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