Can't do simple query or drop table due to out of memory error, but pg_locks return no lock

I received this out of memory error when trying to drop a large table (70GB including index) but couldn't identify the root cause from pg_locks view

DROP TABLE big_table;

ERROR:  out of shared memory
HINT:  You might need to increase max_locks_per_transaction.

I had this error several times when updating this table and has increased max_locks_per_transaction from 64 to 100. The updating went smoothly and I could do some query on it with no issue for a while. But a day later, I couldn't do anything with this table anymore. For some reasons, now I have to drop this table but can't do it due to this error, even after I increased max_locks_per_transaction to 150 (the current max_connections is 20). The strange thing is when I tried to find if there's any lock, I didn't note any unusual query.

SELECT relation::regclass, * FROM pg_locks WHERE not granted;
(0 rows)

I could try increase max_locks_per_transaction again but it seems there's other issue that I need to address. Also, this might not be relevant but just in case it's helpful: the script to update the table in question (big_table) had a query to another table which is updated hourly. Anyway, the transaction to update big_table only ran once and has ended by the time I tried to drop it. Both tables are hypertables created with timescaledb. Below is the full view from pg_locks in case it's helpful.

SELECT * FROM pg_locks;

-[ RECORD 1 ]------+----------------
locktype           | relation
database           | 16384
relation           | 12143
page               |
tuple              |
virtualxid         |
transactionid      |
classid            |
objid              |
objsubid           |
virtualtransaction | 4/33
pid                | 344280
mode               | AccessShareLock
granted            | t
fastpath           | t
-[ RECORD 2 ]------+----------------
locktype           | virtualxid
database           |
relation           |
page               |
tuple              |
virtualxid         | 4/33
transactionid      |
classid            |
objid              |
objsubid           |
virtualtransaction | 4/33
pid                | 344280
mode               | ExclusiveLock
granted            | t
fastpath           | t