Flatpak opens to a blank window; no errors in log

I've installed this app, but when I run it, I just get a completely blank window (aside from the headerbar).
If I run from a terminal, there are no error messages, so I have absolutely no leads for troubleshooting.

**Terminal output:**

```
❯ flatpak run org.cockpit_project.CockpitClient

```

**Screenshot:**

Start by reproducing the reported `flatpak run org.cockpit_project.CockpitClient` command and compare the result with the attached screenshot. Inspect the Flatpak application and its startup path for a cause of the blank window, since the issue names no source files or tests. Done means the application opens with visible content and the failure is no longer silent.

Written by the indexing model from the issue text.