A tricky bug has been fixed where atoms were not persisted in the compilation files. The atoms specifying the types were converted into strings in the Ecto Type’s init/1 function at compile-time, and so as we only worked with the strings afterwards, the atoms were not persisted:
https://github.com/mathieuprog/polymorphic_embed/issues/59
Fixed in 3.0.3 thanks to the support of @LostKobrakai on Slack and the contribution of Alessio ! 
