diff --git a/RELEASE_NOTES.md b/RELEASE_NOTES.md
index 3d2f0d821..cfcaa3149 100644
--- a/RELEASE_NOTES.md
+++ b/RELEASE_NOTES.md
@@ -7,6 +7,14 @@ This file contains a high-level description of this package's evolution. Release
 
 ## 4.9.3 - TBD
 
+## Known Issue
+
+* Parallel operation using `mpich 4.2.0` (the default on `Ubuntu 24.04`) results in 'unexpected results' when running `nc_test4/run_par_test.sh`.  This can be fixed by removing `mpich` and associated libraries and development packages and installing `mpich 4.2.2` by hand, or by using `openmpi` provided via `apt`.
+
+## Release Notes
+
+### Release Candidate 2 - TBD
+
 * Provide better documentation for the .rc file mechanism and API. See [Github #2956](https://github.com/Unidata/netcdf-c/pull/2956) for more information.
 * Convert NCZarr V2 to store all netcdf-4 specific info as attributes. This improves interoperability with other Zarr implementations by no longer using non-standard keys. The price to be paid is that lazy attribute reading cannot be supported. See [Github #2836](https://github.com/Unidata/netcdf-c/pull/2936) for more information.
 * Cleanup the option code for NETCDF_ENABLE_SET_LOG_LEVEL\[_FUNC\] See [Github #2931](https://github.com/Unidata/netcdf-c/pull/2931) for more information.