Retention Policy does not drop old series

Hi everyone.
I am running an influxdb container in my own infrastructure. Initially I had the default retention policy, autogen, configured to not delete old data (default configuration). After several months, the number of series had increased to over a million. The influxdb had old series that I no longer needed. So, I have now configured the default retention policy to delete data older than 1 week. This, however, did not delete older series as the SHOW SERIES CARDINALITY query still shows it is over a million (only noticed a decrease of a few tens). I did notice that the data associated with those series were deleted but the series can still be seen. Does the retention policy not drop old series? I even tried restarting the container, but no change in series cardinality.

I am using influxdb:1.7.9-alpine. Retention Policy is set as follows:

> show retention policies
name    duration shardGroupDuration replicaN default
----    -------- ------------------ -------- -------
autogen 168h0m0s 168h0m0s           1        true

The result of SHOW SHARDS:

> show shards
id  database retention_policy shard_group start_time           end_time             expiry_time          owners
--  -------- ---------------- ----------- ----------           --------             -----------          ------
321 tlpd     autogen          321         2021-03-29T00:00:00Z 2021-04-05T00:00:00Z 2021-04-12T00:00:00Z 
325 tlpd     autogen          325         2021-04-05T00:00:00Z 2021-04-12T00:00:00Z 2021-04-19T00:00:00Z 

The shards were more than this before and it currently reflects the correct numbers after the retention policy was applied.

The result of SHOW SERIES CARDINALITY:

> show series cardinality
cardinality estimation
----------------------
8228479

The cardinality should have had decreased to below 2k given the data pushed since 2021-03-29.

I tried looking up the solution and found some related topics, but they provide incomplete answers. e.g.: