Problem:
After patching an Oracle 19.3 GRID_HOME on Oracle Restart setup with 19.5 RU patch [30125133], I was not able to start up Oracle Restart HAS due to this error:

#  $GRID_HOME/bin/crsctl start has
CRS-6706: Oracle Clusterware Release patch level (‘3291738383’) does not match Software patch level (‘724960844’). Oracle Clusterware cannot be started.
CRS-4000: Command Start failed, or completed with errors.

Analysis:
Despite the success of patching GRID_HOME with 19.5 RU went successful, something went wrong during the patching process.
While trying to find a solution, I landed on Oracle Note (Doc ID 1639285.1) which describes a similar problem on a RAC setup, but it didn’t offer a solution for Oracle Restart setup –which is my case. So I thought to write about the solution I followed and worked for me in this post.

Solution:
Running the following commands would fix/complete an in-complete patching of the GRID_HOME on an Oracle Restart setup:
You have to run the following commands with root user while Oracle Restart HAS is stopped:
# $GRID_HOME/crs/install/roothas.sh -unlock
# $GRID_HOME/crs/install/roothas.sh -prepatch 
# $GRID_HOME/crs/install/roothas.sh -postpatch

Oracle Restart HAS will startup automatically after the last command.