Not overly familiar with Liverpool, NOTAM's show a recent level change at Upton @FL170 for the Tipod 1E arrival so perhaps aircraft are flying a shallower descent E-W towards WAL than before. Don't know if there was any previous restriction.
More likely is Liverpool is greatly affected by the runway in use at MAN. MAN has been predominantly using 05 recently so traffic manoeuvring into Liverpool will be kept lower earlier to provide separation.