FATAL sandbox setuid_sandbox_host.cc

Let's assume your AppImage file is here:
/opt/my-application.AppImage

Run:
sudo vim /etc/apparmor.d/my-application

Then paste the following:
abi <abi/4.0>,
include <tunables/global>

profile application "/opt/my-application.AppImage" flags=(unconfined) {
userns,

include if exists <local/my-application>
}

Then run:
sudo systemctl reload apparmor

Now your AppImage should work