We're sorry for the inconvenience! Are you perhaps using an older version of the spine-unity runtime, or created the clips in an old version and re-imported them in a new version?
Newer versions of the runtime automatically preserve user-added events and don't clear all existing events upon reimport (clip re-generation). They add the event string
SpineEvent at every event that comes imported from the Spine skeleton, which will be removed upon clip re-generation. If you have created the clip in an older runtime it will be lacking the event string parameter
SpineEvent and will thus count as a user event. You should only need to clear these events once though.