I want to save a bunch of completed torrent metafile but this feature only work for a single torrent. Thus it become very unproductive if there are many torrents involved.

The mentioned feature is found under Share -> Save .torrent in the Transfers window.

what version of Tixati are you using?
If not the newest v3.24 upgrade to it.
This was recently broken but fixed.
What OS?

Was using 3.22 and earlier version when encountered this issue. After upgrading to 3.24, issue is resolved. Thanks.