vacuum toast loop?

hello - i've a long-running manual vacuum on a big size table. It's many
TB db that has some toast. What is odd is that it keeps looping back on
the same toast / index, eg.

INFO: 00000: "pg_toast_17283": removed 178956683 row versions in 52264585
pages
DETAIL: CPU 737.22s/1145.35u sec elapsed 53850.35 sec.
LOCATION: lazy_vacuum_heap, vacuumlazy.c:1169
INFO: 00000: scanned index "pg_toast_17283_index" to remove 178956681 row
versions
DETAIL: CPU 89.90s/215.38u sec elapsed 4121.92 sec.
LOCATION: lazy_vacuum_index, vacuumlazy.c:1335
INFO: 00000: "pg_toast_17283": removed 178956681 row versions in 43893618
pages
DETAIL: CPU 421.92s/1084.34u sec elapsed 23879.84 sec.
LOCATION: lazy_vacuum_heap, vacuumlazy.c:1169
INFO: 00000: scanned index "pg_toast_17283_index" to remove 178956683 row
versions
DETAIL: CPU 95.21s/211.57u sec elapsed 3479.92 sec.
LOCATION: lazy_vacuum_index, vacuumlazy.c:1335
INFO: 00000: "pg_toast_17283": removed 178956683 row versions in 43957868
pages
DETAIL: CPU 459.10s/1202.59u sec elapsed 25266.61 sec.
LOCATION: lazy_vacuum_heap, vacuumlazy.c:1169

..and so on. Is this normal? If so, when does the toast vacuum cease?

thanks in advance!

-gleeco