local test of a new Appdata file

This is a follow up from this question on appstream tracker.

I'm trying to test locally a new appdata file I'm contributing for a project. I've generated the AppStream metadata using appstream-compose. The application is visible in Software, but:

• The app icon is not displayed. Instead there is a "blue-gears" icon, which seems a fallback icon.
• No screenshots.
• All details (version, license, etc.) are empty.
• Launch and Remove buttons don't work.

I've launched gnome-software --verbose and here's what I got:

01:29:17:0525 Gs  pushing back entry for search with frescobaldi
01:29:17:0527 Gs  nothing adopted system/*/*/desktop/frescobaldi/*
01:29:17:0532 GsPluginPackageKit ignoring /usr/share/applications/frescobaldi as does not exist
01:29:17:0533 Gs  running refine with dedupe-flags=7 with refine-flags=require-license,require-url,require-description,require-version,require-history,require-setup-action,require-origin,require-menu-path,require-addons,require-provenance,require-icon,require-permissions,require-origin-hostname,require-runtime,require-screenshots,require-categories,require-project-group,require-developer-name,require-kudos,content-rating with timeout=60 on apps system/*/*/desktop/frescobaldi/* took 6ms
01:29:17:0546 Gs  GsApp: [0x7f139c450db0]
kind:                desktop
state:               installed
id:                  frescobaldi
unique-id:           system/*/*/desktop/frescobaldi/*
scope:               system
kudo-percentage:     0
name:                Frescobaldi
match-value:         00050
summary:             LilyPond Music Editor
launchable{desktop-id}: frescobaldi.desktop
reviews:             0
provides:            0
{appstream::source-file}: /usr/share/metainfo/frescobaldi.metainfo.xml
{GnomeSoftware::Creator}: appstream

01:29:17:0549 Gs  content rating system is guessed as PEGI from it_IT.UTF-8
01:29:17:0549 Gs  nothing adopted system/*/*/desktop/frescobaldi/*
01:29:17:0554 GsPluginOdrs got review data for frescobaldi from /home/fede/.cache/gnome-software/odrs/frescobaldi.json
01:29:17:0554 Gs  running refine with dedupe-flags=7 with refine-flags=require-size,require-rating,require-reviews,require-review-ratings,require-runtime with timeout=60 on apps system/*/*/desktop/frescobaldi/* took 4ms
01:29:17:0558 GsPluginShellExtensions silo already valid
01:29:17:0562 Gs  running get-alternates with refine-flags=require-origin,require-provenance,require-origin-hostname with interactive=True with timeout=60 on plugin=flatpak took 12ms
01:30:06:0476 Gs  no refine flags set for transaction
01:30:06:0477 Gs  running launch with dedupe-flags=7 with interactive=True with timeout=60 on plugin=flatpak on apps system/*/*/desktop/frescobaldi/* took 1ms
01:32:52:0372 PK  notify::connected

Find attached the appdata metainfo file.

frescobaldi.metainfo.xml

Please let me know if you can spot any mistake. Thanks!