"flatpak run ..." fails with "bwrap: Can't get type of source /mnt: Permission denied"

[Thomas Bechtold]

When I try to start a flatpak app, I get:

$ flatpak run org.gnome.gitg
bwrap: Can't get type of source /mnt: Permission denied
error: Failed to sync with dbus proxy
$ echo $?
1

I have:
$ flatpak list
Name Application ID Version Branch Installation
Freedesktop Platform org.freedesktop.Platform 21.08.14 21.08 system
Mesa org.freedesktop.Platform.GL.default 21.3.8 21.08 system
openh264 org.freedesktop.Platform.openh264 2.1.0 2.0 system
GNOME Application Platform version 41 org.gnome.Platform 41 system
gitg org.gnome.gitg 41 stable system
Yaru Gtk Theme org.gtk.Gtk3theme.Yaru 3.22 system

ProblemType: Bug
DistroRelease: Ubuntu 22.04
Package: flatpak 1.12.7-1
ProcVersionSignature: Ubuntu 5.15.0-35.36-generic 5.15.35
Uname: Linux 5.15.0-35-generic x86_64
NonfreeKernelModules: zfs zunicode zcommon znvpair zavl icp
ApportVersion: 2.20.11-0ubuntu82.1
Architecture: amd64
CasperMD5CheckResult: pass
CurrentDesktop: ubuntu:GNOME
Date: Fri Jun 10 20:08:35 2022
InstallationDate: Installed on 2022-03-21 (80 days ago)
InstallationMedia: Ubuntu 21.10 "Impish Indri" - Release amd64 (20211012)
RebootRequiredPkgs: Error: path contained symlinks.
SourcePackage: flatpak
UpgradeStatus: Upgraded to jammy on 2022-03-21 (80 days ago)

[Thomas Bechtold (toabctl)]

This seems to happen when I mount something to /mnt before running flatpak:

$ sudo guestmount -a livecd.ubuntu-cpc.ec2-hvm-ebs.vmdk -i --ro /mnt
[sudo] password for tom:
$ flatpak run org.gnome.gitg
bwrap: Can't get type of source /mnt: Permission denied
error: Failed to sync with dbus proxy