How to resolve "error creating output file XXX Permission denied" during logrotate execution

Issue

• The following error occurred during the execution of logrotate.

 logrotate /etc/logrotate.d/tlog 
error: error creating output file /test/testdir/bak/log/tlog.log_2023-06-03: Permission denied

• We can see that the secondary group of user tlog01 is set to tbak_gp, but logrotate still failed due to permission denied.
  The associated settings are as follows:

# cat /etc/logrotate.d/tlog 
/test/testdir/log/tlog.log
{
    daily
    rotate 90
    dateext
    dateformat _%Y-%m-%d
    missingok
    copytruncate
    su tlog01 tlog_gp
    olddir /test/testdir/bak/log
}

# ls -ld /test/testdir/bak/log/
drwxrwxr-x 2 tbak01 tbak_gp 6 Jun 14 14:11 /test/testdir/bak/log/

# id tlog01
uid=1005(tlog01) gid=1005(tlog01) groups=1005(tlog01),1008(tbak_gp)

# cat /etc/group | grep tlog_gp
tlog_gp:x:1006: