Unexpected deadlock across two separate rows, using Postgres 17 and Django's select_for_update() - Mailing list pgsql-general

I'm trying to understand/fix a rare deadlock in my application. Given my limited knowledge, what seems odd to me is that the deadlock involves two processes running exactly the same code/query, each of which (tries to) avoid issues by locking exactly one row for update. In Django-speak, the code does this:

#
# Select-for-update exactly one row by id.
#
qs = Endpoint.objects.select_for_update().filter(id=instance.id)
#
# The above returns a queryset of one row which we loop over:
#
for item in qs:

    ...do stuff with item...

    item.save() 

The deadlock is reported in the Postgres server log like this:

ERROR: deadlock detected
DETAIL: Process 15576 waits for ShareLock on transaction 31053599; blocked by process 16953.
Process 16953 waits for ShareLock on transaction 31053597; blocked by process 15576.
Process 15576: SELECT “paiyroll_endpoint”.“id”, “paiyroll_endpoint”.“op_id”, “paiyroll_endpoint”.“client_id”, “paiyroll_endpoint”.“client_private”, “paiyroll_endpoint”.“netloc”, “paiyroll_endpoint”.“calls”, “paiyroll_endpoint”.“ms”, “paiyroll_endpoint”.“history”, “paiyroll_endpoint”.“current_history” FROM “paiyroll_endpoint” WHERE “paiyroll_endpoint”.“id” = 1 FOR UPDATE
Process 16953: SELECT “paiyroll_endpoint”.“id”, “paiyroll_endpoint”.“op_id”, “paiyroll_endpoint”.“client_id”, “paiyroll_endpoint”.“client_private”, “paiyroll_endpoint”.“netloc”, “paiyroll_endpoint”.“calls”, “paiyroll_endpoint”.“ms”, “paiyroll_endpoint”.“history”, “paiyroll_endpoint”.“current_history” FROM “paiyroll_endpoint” WHERE “paiyroll_endpoint”.“id” = 2 FOR UPDATE
HINT: See server log for query details.
CONTEXT: while locking tuple (7,15) in relation “paiyroll_endpoint”
STATEMENT: SELECT “paiyroll_endpoint”.“id”, “paiyroll_endpoint”.“op_id”, “paiyroll_endpoint”.“client_id”, “paiyroll_endpoint”.“client_private”, “paiyroll_endpoint”.“netloc”, “paiyroll_endpoint”.“calls”, “paiyroll_endpoint”.“ms”, “paiyroll_endpoint”.“history”, “paiyroll_endpoint”.“current_history” FROM “paiyroll_endpoint” WHERE “paiyroll_endpoint”.“id” = 1 FOR UPDATE

How can there be a deadlock between updates to different rows (as per the bolded WHERE clauses)? Have I somehow turned off row-level locks? Is there some additional logging I could enable to try to catch the data needed to root-cause this?

Any help appreciated.

Thanks, Shaheed