What version are you using? On what operating system?

v1.3.0-543-gfdad4fd Linux 64 bit

Can you reproduce using the vpxdec or vpxenc tools? What command line are
you using?

$ ./vpxenc --codec=vp9 --target-bitrate=2500 --threads=0 --cpu-used=2 --ivf -o /dev/null --limit=250 --arnr-maxframes=0 $HOME/video/tearsofsteel-960x400-420.y4m
Pass 1/2 frame  250/251    38152B    1220b/f   30521b/s 2460976 us (101.59 fps)
Pass 2/2 frame  156/131   560496B   16860 ms 9.25 fps [ETA  0:00:13] vpxenc: ../libvpx-golden/vp9/encoder/vp9_encodeframe.c:1856: rd_pick_partition: Assertion `tp_orig < *tp' failed.
Aborted (core dumped)