This bug was fixed in the package initramfs-tools - 0.131ubuntu19.1
--------------- initramfs-tools (0.131ubuntu19.1) disco; urgency=medium
* Patch unmkinitramfs to cat possible lz4 archives first, as lz4 is particular about enforcing .lz4 file extensions when operating on files. LP: #1832108
-- Dimitri John Ledkov <email address hidden> Tue, 11 Jun 2019 16:17:51 +0100
This bug was fixed in the package initramfs-tools - 0.131ubuntu19.1
---------------
initramfs-tools (0.131ubuntu19.1) disco; urgency=medium
* Patch unmkinitramfs to cat possible lz4 archives first, as lz4 is
particular about enforcing .lz4 file extensions when operating on
files. LP: #1832108
-- Dimitri John Ledkov <email address hidden> Tue, 11 Jun 2019 16:17:51 +0100