Yes, it is still reproducible. When I try to VACUUM FULL right now, I get the same error.
This is postgres 9.4. I am new to gdb, but based on what you said, I have the following output:
Breakpoint 1, 0x0000000000768be0 in errfinish ()
(gdb) bt
#0 0x0000000000768be0 in errfinish ()
#1 0x000000000076998c in elog_finish ()
#2 0x0000000000495960 in ?? ()
#3 0x0000000000496075 in heap_tuple_fetch_attr ()
#4 0x0000000000496572 in toast_insert_or_update ()
#5 0x0000000000492ce1 in ?? ()
#6 0x0000000000493733 in rewrite_heap_tuple ()
#7 0x000000000053ebdf in ?? ()
#8 0x000000000053f68e in cluster_rel ()
#9 0x0000000000590a1b in ?? ()
#10 0x0000000000590f9f in vacuum ()
#11 0x000000000068ee77 in standard_ProcessUtility ()
#12 0x00007f50c6b583d4 in ?? () from /usr/pgsql-9.4/lib/pglogical.so
#13 0x000000000068bb17 in ?? ()
#14 0x000000000068caad in ?? ()
#15 0x000000000068d132 in PortalRun ()
#16 0x000000000068979e in ?? ()
#17 0x000000000068ae18 in PostgresMain ()
#18 0x0000000000635d69 in PostmasterMain ()
#19 0x00000000005cd248 in main ()
(gdb) cont