"My s&box UI won't update / is frozen"

You change game state, but the panel on screen never reflects it. A counter stays stale, a modal won't close, a loading bar sits at 0% even though work is progressing. No error, no crash: the UI is simply not re-rendering.

BuildHash() is the only re-render trigger in s&box Razor. The panel recomputes the hash each frame and re-renders only when that integer changes. Any value your markup reads but the hash omits is silently frozen.

Hashing a collection reference or object identity stays constant even as contents mutate, so the UI looks dead while data moves underneath.

Hash everything the markup reads, collection contents, derived display strings (they're cheap), day/date, and every open/closed flag you branch on:

@inherits PanelComponent

@code {
    protected override int BuildHash() => HashCode.Combine(
        Counts.Values.Sum(),    // collection CONTENTS, not the reference
        Game?.Day ?? 0,
        Progress,               // loading bar / time-sliced work
        UIState.ThisPanelOpen,
        UIState.AnyModalOpen
    );
    // HashCode.Combine has NO 9-arg overload - a flat 9th
    // argument is CS1501. Nest instead:
    // HashCode.Combine(HashCode.Combine(a..h), i)
}

Skeleton reminder:

@using Sandbox
@using Sandbox.UI
@namespace YourGame
@inherits PanelComponent

<root>
    @if (Game is not null && UIState.ThisPanelOpen)
    {
        <div class="panel">@Counts.Values.Sum()</div>
    }
</root>

If the panel type itself can't be found from C#, fix @namespace first: razor-namespace-trap.

Razor does not diff the full tree every frame. It treats BuildHash() as a dirty bit: same int → skip rebuild. Content-sensitive hashes (sums, counts, flags, progress) change when the player-visible state changes, so the markup runs again and the screen catches up.