Unprecedented change in the position of four radio sources

Astrometric positions of radio-emitting active galactic nuclei (AGNs) can be determined with sub-milliarcsec accuracy using very long baseline interferometry (VLBI). The usually small apparent proper motion distant extragalactic targets allow us to realize the fundamental celestial reference frame VLBI observations. However, long-term astrometric monitoring may reveal extreme changes in some AGN positions. Using new observations 2018-2021, we show here that four radio sources (3C48, CTA21, 1144+352, 1328+254) have a dramatic shift their by 20-130 milliarcsec over two decades. For all sources, positional is caused structure change.