As you can see in the picture I tried to place a stone block on top of the portal crown block in creative and got the error texture. I repeated this using dirt as well, and then glass confirming that it also happens with transparent blocks.

It does not happen with another crown block. That gives you a rather nice pillar . . . but if you try to use them as a normal fence they don't hook together, or attach to other wall blocks.

Here are some more images:

I don't think this is what you had in mind. lol

Good find. I need to look at my wall models some more.

Unable to load model: 'dimdungeons:block/template_wall_side_tall' referenced from: dimdungeons:block_portal_crown#east=none,north=none,south=none,up=true,waterlogged=true,west=none: java.io.FileNotFoundException: dimdungeons:models/block/template_wall_side_tall.json

oh that's bad

Should be fixed in 1.11, coming out soon. Thanks again for the report. It's a miracle this block ever worked because the more I looked, the more I found that was wrong.