I think this is a bug and it appears to only be in the Post.aspx view. To summarize, when the exact same web part is added to the POST.aspx page as well as the /Forms/AllItems.aspx page, it crashes on the first and works on the latter.
To try and keep this short I'll be simple
1) Create a Team Site with a contacts app
2) Create a Blog SUB site with a contacts app and a document app
3) In the team site, create a new Site Column that is a Lookup to it's Contact app (based on Last Name Linked Field)
4) In the sub BLOG site, create a new Site Column that is a Lookup to it's Contact app (based on Last Name Linked Field)
5) In the sub BLOG site, add both the Parent Team Site Lookup and the Blog Site Lookup as an "Existing Column" to both the POST and the Document Apps.
so at this point, you should have a blog sub site with a Post app and a Document app that have 2 new columns added: One is the Contact lookup column from the Parent site, the other is the Contact Lookup column from the local Blog site.
Let the fun begin...
6) On the Blog post details page (the page that comes up when you click on the title of an individual BLOG post), add 2 new web parts.... one is the existing "Post" library, which means you would have the same info just in a different view) and the other web part is the existing "Document" library. For each newly added Web part.... edit the current view and make sure to include the newly added Lookup columns.
7) On the Blog's Document library page (the page that comes up when you view everything in this app), add 2 new web parts.... one is the existing "Post" library, and the other web part is the existing "Document" library (which is a duplicate of the already existing web part). For each newly added Web part.... edit the current view and make sure to include the newly added Lookup columns.
So at this stage, you have Post Page that has the original Post web part + added second Post web part + document library web part. You also have a Document Library page that has the original Document web part + added a second Document Web Part + Post Web part.
What you should see is that the actual "POST" page (/List/Posts/Post.aspx?ID=n) will not even display the original untouched web part. The added Document web part (with the new columns showing) will show and the Contact Linking works. The second occurrence of the Post Web part (which includes the new lookup columns) crashes and displays an error on the screen.
If you open up the Document Library, you will see the original untouched web part working, and BOTH of the newly added web parts which includes the exact same "Post" + new Lookup columns as above.
... so long story short... the same web part for the same object library with the same display columns works in the _layouts/15/start.aspx#/myDocs/Forms/AllItems.aspx however does not work in the the /_layouts/15/start.aspx#/Lists/Posts/Post.aspx
Would this be a bug?