There has been a few threads on this most notably Caught exception trying to convert extra data attribute 'originallyAvailableAt' with type 1 and value <Date> ~ bad lexical cast: source type value could not be interpreted as target where its confirmed its benign and will be fixed in a future PMS update.
Also, I think I remember it being mentioned its related to having Prefer local metadata enabled on your library can cause this error to show in the logs.
