FRR 9.0.1 in VyOS build from git just now uses an FRR built from 9.0.1-51-g8a6b43262. This version of FRR dies upon issuing a vtysh -c "show rpki prefix $prefix".
This is apparently fixed in FRR 9.0.1-61-gd5d6be1d8.
Given that this can be a nasty surprise when dealing with RPKI, it might be good to rebuild FRR from the newest stable/9.0.