Anyway and if not about to erase your L5 eMMC by using JumpDrive we do not need this tool at all, not for our intended flashing purpose here, I think, therefore I would like to either propose or introduce to you another method (without involving JumpDrive tool, kind of old school method, after ensured that your L5 already connected through: uuu -lsusb).
Perhaps, I hope so, you would like, @librem5, to follow this official guide/reference and rename respectively, actually use flash_librem5r4.lst (instead of using flash_devkit.lst or, here just for example, purism-librem5.lst from within JumpDrive extract folder)?
If your answer is yes (as I didn’t test this because I need to make backup first, but not today) please proceed with (above linked guide adjusted from my side so double check for eventual errors):
Please make fresh (as of today) download of uuu Scripts:
mkdir Librem5_uuu_files
Note, no need to download the Recovery Image while it be included afterwards within Flash_Librem5 folder:
https://arm01.puri.sm/job/u-boot_builds/job/uboot_librem5-recovery_build/
Second note, there is, as well, no need to download the Latest Image:
luks Build 10655: https://arm01.puri.sm/job/Images/job/Image%20Build/10655/
or plain Build 10652: https://arm01.puri.sm/job/Images/job/Image%20Build/10652/
Now it is time for me to make above long story shorter (as partially tested it) and get it done:
cd /home/path-to-your-workspace/Downloads
mkdir Flash_Librem5
cd /home/path-to-your-workspace/.../librem5-flash-image/
sudo ./scripts/librem5r4-flash-image --variant plain --dir /home/path-to-your-workspace/Downloads/Flash_Librem5 --skip-cleanup --skip-flash
cd /home/path-to-your-workspace/Downloads/Flash_Librem5
ls -la
As present there (shown): librem5r4.img is ready to be used as is (no need to “unpack the image”).
It is time to connect your Librem 5 and proof if everything ready:
uuu -lsusb
Now, actually only when you are ready, please execute:
uuu flash_librem5r4.lst
or (if required and probably preferably):
sudo uuu flash_librem5r4.lst
P.S. @librem5, if your Librem 5 survive this procedure (non-torture), I’ll follow your live environment steps gladly 
!?
P.P.S. Partial proof of above from my side:
sudo ./scripts/librem5r4-flash-image --variant plain --dir /home/path_of_yours/Downloads/Flash_Librem5 --skip-cleanup --skip-flash
2022-03-19 10:33:35,352 INFO Looking for librem5r4 plain byzantium image
2022-03-19 10:33:38,771 INFO Found disk image Build 10652 ‘plain librem5r4 byzantium image’ from Sat Mar 19 01:49:27 2022
2022-03-19 10:33:40,446 INFO Found uboot Build 82 from Fri Sep 10 20:19:03 2021
2022-03-19 10:33:40,446 INFO Downloading to /home/path_of_yours/Downloads/Flash_Librem5
2022-03-19 10:33:41,021 INFO Downloading image from https://arm01.puri.sm/job/Images/job/Image%20Build/10652/artifact/librem5r4.img.xz
2022-03-19 10:38:10,350 INFO Calculating sha256sum of /home/path_of_yours/Downloads/Flash_Librem5/librem5r4.img
2022-03-19 10:38:58,816 INFO Downloading uboot from https://arm01.puri.sm/job/u-boot_builds/job/uboot_librem5_build/82/artifact/output/uboot-librem5/u-boot-librem5.imx