Mention known issues in release notes. (#31088)

CHANGES.md

@@ -84,6 +84,7 @@
 
 * Fixed locking issue when shutting down inactive bundle processors. Symptoms of this issue include slowness or stuckness in long-running jobs (Python) ([#30679](https://github.com/apache/beam/pull/30679)).
 * Fixed logging issue that caused silecing the pip output when installing of dependencies provided in `--requirements_file` (Python).
+* Fixed pipeline stuckness issue by disallowing versions of grpcio that can cause the stuckness (Python) ([#30867](https://github.com/apache/beam/issues/30867)).
 
 ## Security Fixes
 * Fixed (CVE-YYYY-NNNN)[https://www.cve.org/CVERecord?id=CVE-YYYY-NNNN] (Java/Python/Go) ([#X](https://github.com/apache/beam/issues/X)).
@@ -144,6 +145,7 @@
 
 * In Python pipelines, when shutting down inactive bundle processors, shutdown logic can overaggressively hold the lock, blocking acceptance of new work. Symptoms of this issue include slowness or stuckness in long-running jobs. Fixed in 2.56.0 ([#30679](https://github.com/apache/beam/pull/30679)).
 * WriteToJson broken in languages other than Java (X-lang) ([#30776](https://github.com/apache/beam/issues/30776)).
+* Python pipelines might occasionally become stuck due to a regression in grpcio ([#30867](https://github.com/apache/beam/issues/30867)). The issue manifests frequently with Bigtable IO connector, but might also affect other GCP connectors. Fixed in 2.56.0.
 
 # [2.54.0] - 2024-02-14
 
@@ -274,6 +276,7 @@ as a workaround, a copy of "old" `CountingSource` class should be placed into a
 
 * MLTransform drops the identical elements in the output PCollection. For any duplicate elements, a single element will be emitted downstream. ([#29600](https://github.com/apache/beam/issues/29600)).
 * Some Python pipelines that run with 2.52.0-2.54.0 SDKs and use large materialized side inputs might be affected by a performance regression. To restore the prior behavior on these SDK versions, supply the `--max_cache_memory_usage_mb=0` pipeline option. (Python) ([#30360](https://github.com/apache/beam/issues/30360)).
+* Users who lauch Python pipelines in an environment without internet access and use the `--setup_file` pipeline option might experience an increase in pipeline submission time. This has been fixed in 2.56.0 ([#31070](https://github.com/apache/beam/pull/31070)).
 
 # [2.51.0] - 2023-10-03