  We present observational evidence of late-time interaction between the ejecta
of the hydrogen-poor Type Ib supernova (SN) 2019yvr and hydrogen-rich
circumstellar material (CSM), similar to the Type Ib SN 2014C. A narrow
H{\alpha} emission line appears simultaneously with a break in the light-curve
decline rate at around 80-100 d after explosion. From the interaction delay and
the ejecta velocity, under the assumption that the CSM is detached from the
progenitor, we estimate the CSM inner radius to be located at ~6.5-9.1 {\times}
10^{15} cm. The H{\alpha} emission line persists throughout the nebular phase
at least up to +420 d post-explosion, with a full width at half maximum of
~2000 km/s. Assuming a steady mass-loss, the estimated mass-loss rate from the
luminosity of the H{\alpha} line is ~3-7 {\times} 10^{-5} M_\odot yr^{-1}. From
hydrodynamical modelling and analysis of the nebular spectra, we find a
progenitor He-core mass of 3-4 M{_\odot}, which would imply an initial mass of
13-15 M{_\odot}. Our result supports the case of a relatively low-mass
progenitor possibly in a binary system as opposed to a higher mass single star
undergoing a luminous blue variable phase.
