Issue with sync (mapper_parsing_exception)

Hello,

We have an issue on several of our sites with the synchronization of posts to our ElasticSearch instance.
This issue seems to be a problem with synchronizing the taxonomy terms of the posts.

The error we get is:

9552 (Post): [mapper_parsing_exception] object mapping for [terms.themas.facet] tried to parse field [facet] as object, but found a concrete value

Almost every single post triggers this error. It also triggers on multiple taxonomies.

Can you help us with this problem?