  We found that the SU UMa-type dwarf nova NY Ser in the period gap [orbital
period 0.097558(6) d] showed standstills twice in 2018. This is the first clear
demonstration of a standstill occurring between superoutbursts of an SU
UMa-type dwarf nova. There was no sign of superhumps during the standstill, and
at least one superoutburst directly started from the standstill. This provides
strong evidence that the 3:1 resonance was excited during standstills. This
phenomenon indicates that the disk radius can grow during standstills. We also
interpret that the condition close to the limit of the tidal instability caused
early quenching of superoutbursts, which resulted substantial amount of matter
left in the disk after the superoutburst. We interpret that the substantial
matter in the disk in condition close to the limit of the tidal instability is
responsible for standstills (as in the high mass-transfer system NY Ser) or
multiple rebrightenings (as in the low mass-transfer system V1006 Cyg).
