Done that an I have now a diff. situation.
demsg -w shows now less errors (now complaining about no support for DPO or FUA).
Also telnet does work now.
But eMMC is still not available as storage.
Is LUKS preventing this?
Perhaps important info:
I simply switched over the USB cable to another port.
Jumpdrive kept running and did not complain about the interruption.
Okay, then from here, you should be able to use step 16 and up of @Lliure’s guide to access the encrypted partition.
Some problems dissapear while waiting 
.
I was looking on the host for some mount utilities and tadaa a popup appeared asking for my Luks key.
Entered it and “voila”, now I have access to eMMC.
Thank you for helping and solving my issue(s). 
No. Jumpdrive is just exporting a block device (or two block devices, if you have a uSD card inserted in your phone). There need be no file system at all. It’s up to the host computer to interpret the data. (So, yes, the exact commands to do on the host computer will depend on whether LUKS is in use on the eMMC drive. Regardless though the /boot partition is not encrypted and should work even if LUKS is giving you grief.)
Thanks for explaining.
As you have seen, I managed to overcome my issues.
Once you know how to do it, it’s a piece of cake to backup and restore an image.
My second L5 is now a complete identical copy of my orriginal one.
As I wanted to have a ‘factory default image’ I made an image from the third (new) L5 before going through the very first start up procedure of the L5.
Restoring this ‘default’ image is less time consuming measured against flashing the L5
One worrying aspect I had was about the old L5 having a Redpine module while the new L5’s have a Sparklan module.
But this is a non-issue.
The OS picks this up without a hassle.
I do have another question about using Jumpdrive, but I will create a new thread for it.