Complex sentence: Until Herring joined the band, the lineup had fluctuated in a veritable rotating cast of performers, however, after joining, the bandmates solidified into a lineup which remained largely constant for the next 5 years.
Split into simpler sentences: Until Herring joined the band, the lineup had fluctuated in a rotating cast of performers. However, after joining, the bandmates solidified into a lineup which remained largely constant for the next 5 years.