Hey,
This definitely seems to be a weird issue. From what I could understand, I would recommend the following:
You have already mentioned that you tried changing the DNS at loopia.se’s DNS to ns1.bluehost.com and ns2.bluehost.com, but do you know if the DNS propagation had completed? What I mean by that is, you could actually ping your website MyPrimaryDomain.se to the IP address that Bluehost ha provided you or were you able to check you were getting the results from Bluehost provider name servers. Normally once you change the name server, it takes anywhere from 2-3 hours to 72 hours for DNS changes to reflect, depending on your ISP.
If you are not entirely sure how that works, you can just connect with the Bluehost support team and they should be able to help. It seems since you are not able to open Bluehost’s dashboard, they should be the correct team to help you out with this.
Also on your question on the change of domain name in WordPress, you can even validate that from phpMyAdmin, if Bluehost is providing you with the same.
Do let us know if this helped.
