Add note on tiling usage in 4.2.1

source/changes.rst

@@ -24,6 +24,11 @@ List of the main bugfixes in the new 4.2.1 release - May 2023
 
 **High Performance Computing (HPC)**
 
+.. note::
+
+    Several fixes have been made to the tiling introduced at 4.2.0 (`ln_tile = .TRUE.`), but users may still encounter bugs when using this functionality (disabled by default).
+    Improvements to the robustness and performance of the tiling will be available with the next major release of NEMO.
+
 - Enable NEMO compilation using single-precision variable (:mergereq:`171`)
 - Fix NEMO compilation when using MPI2 option (:mergereq:`97`) and bugfix in configurations without MPI use (:mergereq:`167`)
 - Demonstration of mixed-precision compilation using key_single (ORCA2 only) (:mergereq:`261`)