diff --git a/Plugins/org.secc.FamilyCheckin/Cache/CheckinCache.cs b/Plugins/org.secc.FamilyCheckin/Cache/CheckinCache.cs
index 01ca8fc17..72003e9f5 100644
--- a/Plugins/org.secc.FamilyCheckin/Cache/CheckinCache.cs
+++ b/Plugins/org.secc.FamilyCheckin/Cache/CheckinCache.cs
@@ -176,8 +176,11 @@ private static List<string> UpdateKeys( Func<List<string>> keyFactory, string en
                 var now = DateTime.UtcNow;
                 var currentKeys = AllKeys();
 
-                // If within throttle window and we have existing keys
-                if ( currentKeys.Any() && ( now - _lastKeysRefreshUtc ) < KeysRefreshInterval )
+                // If within the throttle window, serve the cached key list (applying ensure/remove below).
+                // An empty list can be a valid answer (e.g. overnight, before the day's first check-in) and must
+                // still be throttled; otherwise every caller re-runs keyFactory(), which may be an expensive DB query
+                // (e.g., Attendance keyFactory can trigger a full Attendance scan that returns zero rows).
+                if ( ( now - _lastKeysRefreshUtc ) < KeysRefreshInterval )
                 {
                     bool modified = false;
 
diff --git a/Plugins/org.secc.FamilyCheckin/README.md b/Plugins/org.secc.FamilyCheckin/README.md
index f172872d9..cb2fc1de4 100644
--- a/Plugins/org.secc.FamilyCheckin/README.md
+++ b/Plugins/org.secc.FamilyCheckin/README.md
@@ -127,6 +127,23 @@ Quartz `IJob`s (both `[DisallowConcurrentExecution]`); scheduled in Rock, not se
 |------------|---------|
 | `CheckinGroupFieldType` | Picks a single or (configurably) multiple check-in groups; stores `Group.Guid`. Backed by `CheckinGroupPicker` and `CheckinGroupFieldAttribute`. |
 
+### Caching
+
+`CheckinCache<T>` — subclassed by `AttendanceCache`, `OccurrenceCache`, and
+`MobileCheckinRecordCache` — keeps a per-type **key list** in `RockCache` (region `AllItems`, key
+`{TypeName}:All`) next to the cached entities, so `All()` / `AllKeys()` can enumerate without a DB
+round trip. Each subclass supplies a `keyFactory` that rebuilds that list from the database.
+`CheckinKioskTypeCache` is **not** part of this layer — it uses Rock's own `ModelCache`.
+
+**Key-list refresh throttling (PR #281):** key-list refreshes are throttled to once per 10 seconds,
+per cache type, per web-farm node — **including when the cached list is empty**. An empty list is a
+valid state (overnight, before the day's first check-in), and refreshing on every call re-ran
+`keyFactory()` every time; for `AttendanceCache` that is a full `dbo.Attendance` scan returning zero
+rows. Tradeoff: after a cache clear or flush during active check-in, `AllKeys`-derived views
+(attendance / occupancy) can read empty for up to 10 seconds before self-healing. Accepted — the
+`ensureKey` / `removeKey` paths still apply inside the throttle window, so individual check-ins are
+not lost.
+
 ## Dependencies & Integrations
 
 - **Rock:** check-in engine (`CheckInState`, `CheckInActionComponent`), workflow engine,