If the issue started after these were updated (update from Feb 20)
[2021-02-20T09:31:33+0100] [ALPM] upgraded util-linux (2.36.1-3 -> 2.36.2-1)
[2021-02-20T09:31:33+0100] [ALPM] upgraded widevine (90.0.4412.3-1 -> 90.0.4421.5-1)
[2021-02-20T09:31:33+0100] [ALPM] upgraded tar (1.33-1 -> 1.34-1)
[2021-02-20T09:31:33+0100] [ALPM] upgraded sane (1.0.31-1 -> 1.0.32-1)
[2021-02-20T09:31:34+0100] [ALPM] upgraded google-chrome (90.0.4412.3-1 -> 90.0.4421.5-1)
[2021-02-20T09:31:34+0100] [ALPM-SCRIPTLET] [0;32m To have better integration with KaOS
[2021-02-20T09:31:34+0100] [ALPM-SCRIPTLET] [0;32m Select Use GTK+ theme, this will follow your KDE settings
[2021-02-20T09:31:34+0100] [ALPM] upgraded imagemagick (6.9.11.62-1 -> 6.9.12.0-1)
[2021-02-20T09:31:34+0100] [ALPM] upgraded kpmcore (20.12.2-1 -> 20.12.2-2)
[2021-02-20T09:31:35+0100] [ALPM] upgraded kpmcore-debug (20.12.2-1 -> 20.12.2-2)
[2021-02-20T09:31:35+0100] [ALPM] upgraded libinih (52-1 -> 53-1)
[2021-02-20T09:31:35+0100] [ALPM] upgraded libuv (1.40.0-1 -> 1.41.0-1)
[2021-02-20T09:31:35+0100] [ALPM] upgraded xdg-desktop-portal (1.8.0-1 -> 1.8.1-1)
[2021-02-20T09:31:35+0100] [ALPM] upgraded xfsprogs (5.10.0-1 -> 5.10.0-2)
Then sane could be what caused it.
Since this is also in the log:
[2020-09-03T08:50:02+0200] [ALPM] upgraded sane (1.0.30-2 -> 1.0.31-1)
meaning, you should have the sane 1.0.31 still in your cache. You can test if new sane is the problem by installing older with:
sudo pacman -U /var/cache/pacman/pkg/sane-1.0.31-1-x86_64.pkg.tar.zst
Best to reboot after downgrading, and test your scanner, please report back if that fixes it.