Maybe its becaus I am on The Center map. DinoSpawnEntriesMonsterIsland_C is the Half-Burnt-Island, because before I added a Vulture spawner, which worked.
I don't have another container for this spawn, the line is also the first one in the ini.
Did some testing and it looks like the FE dinos are map restricted. I can use the "summon " command for all the dinos which would also spawn on The Island (Rex, Trike, Bronto, Carno, Raptor,...) but I cannot summon the Wyvern.
On the other hand I can summon Zombie-Wyvern on SE but no Bone Rex.
Here is my theroy: The Bone Dinos have been added to the alpha spawns (at least the aggressive ones), which would spawn those dinos on most of the other maps as well if they use the same spawnes, including SE. For the bone dinos to not spawn on SE (or other maps) there was a restiction added, resticting the Bone Dino spawns to The Island (except the Bone Wyvern).
And I think if the "summon" command for a dino does not work, spawns will also not
Thanks for the help @stoni and @norman!
For all those who want to add spawns on the center, here the small list of The Island spawns which I have tested and work on The Center: