Unable to get a list of updates: remote lvfs has no cache signature

Ubuntu Software (aka Gnome Software) on Ubuntu 18.04 has started giving the error message: Unable to get a list of updates: remote lvfs has no cache signature

This issue started recently and, based on a bit of online research, it may be related to Linux Vendor Firmware Service (LVFS) and the fwupd application.

Here are the installed fwupd packages:

~$ apt list --installed | grep fwupd
fwupd/bionic-updates,now 1.2.10-1ubuntu2~ubuntu18.04.3 amd64 [installed]
fwupd-signed/bionic-updates,now 1.10~ubuntu18.04.3+1.2.10-1ubuntu2~ubuntu18.04.3 amd64 [installed,automatic]
fwupdate/bionic-updates,now 12-7~ubuntu18.04.3 amd64 [installed]
fwupdate-signed/bionic-updates,now 12-7~ubuntu18.04.3 amd64 [installed]
libfwupd2/bionic-updates,now 1.2.10-1ubuntu2~ubuntu18.04.3 amd64 [installed,automatic]

and

~$ snap list | grep fwupd
fwupd 1.4.2 2084  latest/stable    richard-hughes  classic

Update 22-Oct-2020: From the discussions below it seems like this warning pops up for a few people for fwupd versions from 1.3.x, so this issue may not be directly due to whether fwupd is installed via snap or apt. Instead, it may be due a combination of having a 1.3.x+ version of fwupd and using a specific device/vendor.

I believe I found the answer after a bit of trial and error. I seem to have both the snap and apt versions of fwupd installed. Removing the fwupd snap version seems to fix the warning message:

snap remove fwupd

However, I don't believe this warning is causing any problems as it seems to be due to misconfiguration on the firmware vendor side. At worst, this warning means that you won't get firmware updates automatically for the affected devices.

My snap fwupd version number (1.4.2) was newer than apt version number (1.2.10), so I decided to just keep the snap version and ignore the warning message.

Open terminal and try this command

fwupdmgr --force refresh

From man page:

--force Force the action by relaxing some runtime checks

refresh [FILE FILE_SIG REMOTE-ID] Refresh metadata from remote server