The Content on the Fly feature enables creating new content objects while editing an existing one. The selected ones are then embedded to the content.
However, together with the Solr bundle - the embedding can fail so that the landing is left pending to "Loading..." state. This is due to content not being available in the Solr index when the interface embeds it.
With the autocommit feature, it is not guaranteed that the content will be in place in the index at publish time. Content would need to be forcefully committed to guarantee at this point.
Example and steps to reproduce presented in screencast here: https://youtu.be/O6Jwld8lan4