When generating fully qualified links, Episerver will choose host names with a specific defined culture over ones without. In your case, episerver would attempt to write all URLs using the wildcard and so would be unable to create a fully qualified link.
The easiest way to resolve this would be to set up an additional host entry with the domain you'd like to use for URL generation and the language defined as EN. This will allow you to keep your wildcard and still give Episerver a domain to use when creationg full URLs.
and don't throw away wildcard mapping, as this might become handy when scheduled jobs will require tt generate urls (if any).
This issue https://world.episerver.com/support/Bug-list/bug/CMS-9871 might be related to your case. It is resolved and is planned to be part of next release (probably in a weeks time frame) unless QA finds any issues with the fix.
We're getting this weird error when saving our current site bindings, if we remove the wildcard definition the error doesn't occur anymore. However removing the wildcard isn't possible in our situation. We have a few other hosts that are using the wildcard and the primary language doesn't work properly without it being assigned to the wildcard.
Our bindings looks like this:
* en http
Thanks in advance :)