PostgreSQL 16.6 , query stuck with STAT Ssl, wait_event_type : IPC , wait_event : ParallelFinish

Hi

a query is stuck with the above, it seems it waits for parallel worker to finish, however , there are no parallel works running :

postgres@[local]/dynacom=# SELECT application_name, backend_type, backend_start,xact_start,query_start,wait_event_type, wait_event ,state FROM pg_stat_activity;
application_name |         backend_type         |         backend_start         |          xact_start           |          query_start          | wait_event_type |     wait_event      | state   
------------------+------------------------------+-------------------------------+-------------------------------+-------------------------------+-----------------+---------------------+--------
                 | autovacuum launcher          | 2024-11-29 17:48:50.92935+02  |                               |                               | Activity        | AutoVacuumMain      |  
                 | logical replication launcher | 2024-11-29 17:48:50.929496+02 |                               |                               | Activity        | LogicalLauncherMain |  
DBMIRROR         | client backend               | 2025-05-31 19:04:16.724305+03 | 2025-05-31 19:05:21.686093+03 | 2025-05-31 19:05:21.909936+03 | IPC             | ParallelFinish      | active
                 | client backend               | 2025-05-31 23:31:30.030806+03 |                               | 2025-05-31 23:35:05.045573+03 | Client          | ClientRead          | idle
psql             | client backend               | 2025-05-31 23:29:33.863485+03 | 2025-05-31 23:35:09.322972+03 | 2025-05-31 23:35:09.322972+03 |                 |                     | active
RXMLFVSLS        | client backend               | 2025-05-31 23:32:37.351131+03 |                               | 2025-05-31 23:35:09.295221+03 | Client          | ClientRead          | idle
psql             | client backend               | 2025-04-28 16:59:55.968442+03 |                               | 2025-05-27 16:43:56.338228+03 | Client          | ClientRead          | idle
                 | background writer            | 2024-11-29 17:48:50.916876+02 |                               |                               | Activity        | BgWriterMain        |  
                 | archiver                     | 2024-12-03 18:57:36.447067+02 |                               |                               | Activity        | ArchiverMain        |  
                 | checkpointer                 | 2024-11-29 17:48:50.916648+02 |                               |                               | Activity        | CheckpointerMain    |  
                 | walwriter                    | 2024-11-29 17:48:50.928789+02 |                               |                               | Activity        | WalWriterMain       |  
(11 rows)

postgres@[local]/dynacom=#

So, I will terminate this backend now to get the system working again, we are curious why this happened, our system serves daily 22M+ transactions, this is Saturday night hence the low traffic.

postgres@smadb:~$ lsb_release -a
No LSB modules are available.
Distributor ID: Debian
Description:    Debian GNU/Linux 12 (bookworm)
Release:        12
Codename:       bookworm
postgres@smadb:~$ psql -Aqt -c 'select version()'
PostgreSQL 16.6 on x86_64-pc-linux-gnu, compiled by gcc (Debian 12.2.0-14) 12.2.0, 64-bit
postgres@smadb:~$