Someone tried to use UTL_FILE.FOPEN in a stored procedure to operate a file, but it sometimes failed with ORA-29283.
ORA-29283: invalid file operation: nonexistent file or path 
ORA-06512: at "SYS.UTL_FILE", line 536
In this case, it's a newly created RAC database, applications usually connect to the database through SCAN VIP. Which means, the store procedure may be executed on node 1 or node 2, we are not sure.
After investigating both DB servers, I found the file path /reports that user tried to open is not existing on the second DB server. That why it sometimes (50% chances) failed to open the file.
To solve ORA-29283 in a RAC system is to share the folder among all DB servers in the same cluster, and make sure all instances are able to see the same directory.
In our case, the directory object RPT_PATH points to /reports, we should make both nodes share /reports folder, either using ACFS (ASM Cluster File System), NFS (Network File System) or GPFS (General Parallel File System).
To prevent ORA-29283, please make sure the folder has already shared on all nodes before we create a directory object in a RAC database.