Updated Known Issues page for urgent DNS caching information

Author: goergenj

articles/ai-services/speech-service/known-issues.md

@@ -39,6 +39,7 @@ This table lists the current known issues for the Text-to-Speech feature.
 | 2002   | TTS Avatar | Missing parameters | TTS Avatar parameters "avatarPosition" and "avatarSize" not supported in Batch synthesis. | N/A | June 9, 2025 |
 | 2003   | TTS Avatar | Missing Blob file names | The 'outputs': 'result' url of Batch avatar synthesis job doesn't have the blob file name. | Customers should use 'subtitleType = soft_embedded' as a temporary workaround. | June 9, 2025 |
 | 2004   | TTS Avatar | Batch synthesis unsupported for TTS | Batch synthesis for avatar doesn't support bring-your-own-storage (BYOS) and it requires the storage account to allow external traffic. | N/A | June 9, 2025 |
+| 2005   | Service | DNS cache refresh before end of July 2025  | Due to compliance reasons, the legacy Speech TTS clusters in Asia are removed on July 31st, 2025. All traffic is migrated from the old IPs to the new ones.<br>Some customers are still accessing the old clusters even after DNS redirection has been completed. This indicates that some customers may have persistent local or secondary DNS caches. | To avoid service downtime, please refresh the DNS cache before the end of July 2025. | July 24, 2025 |
 
 ## Active known issues speech SDK/Runtime