diff --git a/silabs-multiprotocol/CHANGELOG.md b/silabs-multiprotocol/CHANGELOG.md
index c688df7e9..288ef8311 100644
--- a/silabs-multiprotocol/CHANGELOG.md
+++ b/silabs-multiprotocol/CHANGELOG.md
@@ -17,6 +17,13 @@
 - Declare the `/dev/net/tun` device used by OpenThread Border Router.
 - The app image is unchanged from 2.4.5.
 
+> [!WARNING]
+> Known issue on Home Assistant OS 18 and later: `otbr_firewall: false` makes
+> the OpenThread Border Router start script call `ip6tables-legacy`, which
+> fails because the kernel no longer provides the legacy IPv6 filter table.
+> `otbr-agent` then exits with code 3 in a loop and Thread stops working.
+> Keep `otbr_firewall` set to `true` (the default).
+
 ## 2.4.5
 - Support Home Assistant Connect ZBT-1.
 
diff --git a/silabs-multiprotocol/DOCS.md b/silabs-multiprotocol/DOCS.md
index 1923a4259..cfbede575 100644
--- a/silabs-multiprotocol/DOCS.md
+++ b/silabs-multiprotocol/DOCS.md
@@ -84,6 +84,16 @@ App configuration:
 | otbr_log_level     | Set the log level of the OpenThread BorderRouter Agent     |
 | otbr_firewall      | Enable OpenThread Border Router firewall to block unnecessary traffic |
 
+> [!WARNING]
+> On Home Assistant OS 18 and later, keep `otbr_firewall` set to `true` (the
+> default). With the firewall disabled, the OpenThread Border Router start
+> script runs `ip6tables-legacy`, which fails on these systems because the
+> kernel no longer provides the legacy IPv6 filter table. The app log then
+> repeats `ip6tables v1.8.7 (legacy): can't initialize ip6tables table
+> 'filter': Table does not exist` and `otbr-agent exited with code 3`, Thread
+> stops working while Zigbee keeps running. Re-enable the firewall and restart
+> the app to recover.
+
 ## Architecture
 
 The app runs several service internally. This architecture diagram shows what