slow download speed vs other torrent clients.

[rezad1393]

I have qbittorrent installed both on laptop (archlinux/x64) and odroid board (archliniuxarm/arm7vh) and on both when downloading torrents with many seeds I still cant get my max line speed.
my line speed is not high (40Mb/s=~ 5MB/s) and I can get that with transmisison torrent client and even steam game download.
but with qbittorrent I get 2.5MB/s max and usually 1.5MB/s.

any idea what causes this?

[rezad1393]

updae:
it could be the libtorrent used.
I tried on the same laptop archlinux two versions:
one is from flatpak store that has :
Qt: 6.7.3
Libtorrent: 1.2.20.0
Boost: 1.86.0
OpenSSL: 3.1.7
zlib: 1.3.1

and one from archlinux repo that uses:
Qt: 6.8.2
Libtorrent: 2.0.11.0
Boost: 1.87.0
OpenSSL: 3.4.1
zlib: 1.3.1

and I used my mobile tether (that has a better net speed to test)

with a same torrent on a private tracker:
with repo one I get
600KB/s

with the flatpak one I get:
12MB/s.

update:
it is even werider.
the repo one also can go to 12MB/s at almost random start of torrent.
what that means that if I stop the torrent and start it again I can maybe get 12MB/s like the flatpak client.
but it is almost random.

but the flatpak one gets 12MB/s always.

I am now even more confused.