Thomas mentioned in the comment in IMPALA-7184,
Today, the snapshot used to scan in RYW mode is max(propagated timestamp + 1, clean time). If the tablet hasn't been written to recently, a tablet's clean time can fall well before the AHM. If there are no ops in flight, it might be worth considering some other timestamps, e.g. now, now minus the AHM, the current safe time, etc., or escalating a RYW scan to READ_LATEST if the propagated timestamp has passed.