Why creation of FASTRESUME files seems inconsistent - and are they deleted automatically?

[KodeXall]

If I am not mistaken, qBittorrent stores torrent download state in a .fastresume file, both of which are located at

C:\My-Portable-Programs\qBittorrent\profile\qBittorrent\data\BT_backup\

But currently I have e.g.

0594ee9631f9fbbc010ee56123213c024c2f7ab0.fastresume.bvbEPs

074336afb7fe4bc4e8ce01ea569958152f7ba315.fastresume
074336afb7fe4bc4e8ce01ea569958152f7ba315.torrent

0c329dbb56e05d0ac0e947793c1d2977bbfc2fe1.fastresume
0c329dbb56e05d0ac0e947793c1d2977bbfc2fe1.fastresume.xOTovB
0c329dbb56e05d0ac0e947793c1d2977bbfc2fe1.torrent

1d8970b798a012490cae575bf133be13c1e78a61.fastresume
1d8970b798a012490cae575bf133be13c1e78a61.fastresume.dfyiav
1d8970b798a012490cae575bf133be13c1e78a61.fastresume.HtZirY
1d8970b798a012490cae575bf133be13c1e78a61.fastresume.PkHUeN
1d8970b798a012490cae575bf133be13c1e78a61.torrent

So my questions would be:

1] Is a fastresume companion immediately mandatory i.e. is it created from the get-go when a torrent or magnet-link is loaded to qBittorent?

2] Why is there sometimes a derivative / doppelganger fastresume for a particular torrent file with an additional gibberish extension?

3] Why is there sometimes more doppelgangers than just one?

4] Why do I have a derivative

0594ee9631f9fbbc010ee56123213c024c2f7ab0.fastresume.bvbEPs

but not the original

0594ee9631f9fbbc010ee56123213c024c2f7ab0.fastresume

nor even the original

0594ee9631f9fbbc010ee56123213c024c2f7ab0.torrent

file?

6] Under what conditions is a single companion fastresume supposed to be removed automatically?

7] Under what conditions are derivative / doppelgangers supposed to be removed automatically?

8] Can any of them be safely deleted manually, if I deem them as leftovers from long gone download jobs?

9] What happens if I delete them for a job that is still on the list of torrent files in the program?

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(Context: when the BT_backup folder is mirrored with FreeFileSync / RealTimeSync program and I actively download hundreds of torrents, then these fastresume files end up flooding the Recycle Bin of the mirror volume)