Complex sentence: The CVR had slowly been progressing in preserving the line when in the late 1990s they had reached the station site which, however, was not judged worthy of re-opening due to the large amount of other preservation projects being undertaken by the CVR at the time.
Split into simpler sentences: The CVR had slowly been progressing in preserving the line when in the late 1990s they had reached the station site. Unfortunately, the station site site was not judged worthy of re-opening due to the large amount of other preservation projects being undertaken by the CVR at the time.