Using full disk encryption, on a multipath device (in this case FCP) ended up in trying to open/unlock a wrong DM device

This bug was fixed in the package multipath-tools - 0.7.9-3ubuntu2

---------------
multipath-tools (0.7.9-3ubuntu2) eoan; urgency=medium

  * Ensure udebs have the same udev rules as installed systems. LP:
    #1825189

 -- Dimitri John Ledkov <email address hidden> Tue, 21 May 2019 12:34:41 +0100

Next steps is to try to use eoan debian-installer, to see if this is now good or not.

This bug was fixed in the package partman-base - 206ubuntu2

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partman-base (206ubuntu2) eoan; urgency=medium

  * Multipath support:
    - lib/base.sh: is_multipath_part(): Use '-part' as multipath
    disk-partition separator. As otherwise there are differences in
    devices naming between d-i and the installed systems. LP: #1825189

 -- Dimitri John Ledkov <email address hidden> Mon, 17 Jun 2019 15:47:54 +0100

This bug was fixed in the package parted - 3.2-25ubuntu1

---------------
parted (3.2-25ubuntu1) eoan; urgency=medium

  * _device_get_part_path: use -partN for dm partitions. As otherwise
    there are differences in devices naming between what parted creates,
    and what `udevadm trigger` will rename them to. LP: #1825189

 -- Dimitri John Ledkov <email address hidden> Mon, 17 Jun 2019 16:21:08 +0100

@frank stop marking things as done prematurely. this is far from done at the moment.

Also my parted upload is broken!

According to our conversation and a quick test on eoan the initial issue reported by me seemed to be solved - and I just touched the project entry.
But since you mentioned that you discovered further issues, and more packages were added as being affected, I'll leave further updates up to you.

This bug has been reported on the Ubuntu ISO testing tracker.

A list of all reports related to this bug can be found here:
http://iso.qa.ubuntu.com/qatracker/reports/bugs/1825189

So i think i undid all the bogus red-herring fixes that didn't fix anything.

and finally uploaded partman-multipath tools that should now work.

tested with Eoan-proposed it all looks good. Please wait for partman-multipath to publish in eoan release pocket and then retest.

_everything_ should just work. I.e. encrypted lvm on multipath; lvm on multipath; ecnrypted non-lvm on multipath and so on.

I am not sure about lvm, on encrypted, on raid, on multipath. But i believe that should also work.

This bug was fixed in the package partman-multipath - 4ubuntu7

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partman-multipath (4ubuntu7) eoan; urgency=medium

  * finish.d/multipath_partitions: undo init.d/multipath_partitions to use
    in-target -part names, such that later lvm2 can take backup names as
    seen in-target and cryptsetup can generate correct crypttab in the
    initrd. LP: #1825189

 -- Dimitri John Ledkov <email address hidden> Fri, 21 Jun 2019 12:12:03 +0100

Since Ubuntu 19.04 / Disco reached it's end-of-life on January the 23rd:
https://lists.ubuntu.com/archives/ubuntu-announce/2020-January/000253.html
the entry that marks this ticket as affecting 'Disco' is changed to 'Won't Fix'
and with that the overall status adjusted, too.