db size difference on primary and standby

Hi postgres guru out there:

We discovered a disk usage difference between our primary and standby node.

After much investigation, the disk usage difference is caused by some
extra files within the database directory 16432. The extra files are
only found on the standby node, not present on the primary.

In the data directory ("15/data/base/16432"), the extra files do not
seem to belong to any table. Normally, the files correspond to the
column "relfilenode" in the "pg_class" system table; however, when we
compare the entries in that column with the file names, around 600 of
the files do not have a corresponding entry in the "pg_class" table.
The same applies to the files in the "san" tablespace
("pg_tblspc/san/PG_15_202209061/16432").

Has anyone seen this behavior before? Also, we also want to know if
it is safe to remove all those extra files that do not have an entry
in the "pg_class" table?

Thanks in advance
Eric