ALTER TABLE ... DETACH PARTITION just sitting there

AWS RDS Postgresql 12.5.

We've got a table partitioned by month range (FOR VALUES FROM ('2011-07-01')
TO (2011-08-01')), and I've been detaching partitions from oldest to newest,
one at a time. Whenever it's failed due to a FK constraint (and there are
many of them!), I dropped the "same month" partition from TABLE_B, and then
returned and dropped the partition from TABLE_A.

But now, after 17 dropped partitions it's just sitting there on "ALTER TABLE
table_a DROP PARTITION table_a_p2011_07;"  I'm the only user on this test
instance, and validated that nothing else is blocking me.

Are the FK validations what's causing the apparent "hang"?  (EXPLAIN ALTER
TABLE... does not work.)

--
Angular momentum makes the world go 'round.