I'm assuming that the validation test of the switch works fine, and all the upgrade/modify activity (SBP, parameters setting, upgrade of release, upgrade ora_client) was performed on the slave server.
So, all the modification regarding upgrade of DB instances, profile parameters or other changes, I really dont understand the reason you are facing the 12154
In your log:
(HOST = devsvr)
(HOST = 172.16.5.12)
Are you sure that the devsrv hostname is resolved with this IP?
(SID_NAME = DEVDR)
is this value correct?
Are you sure that the DR has this Oracle SID? And in case, how do you perform the copy of DB using different DBSID? Usually, the difference on the DR environment is the logical IP address, mapped with the DNS propagation in case of Disaster Recovery Validation
What about the /oracle/client directory? Try to change the permission to 777
Please take a look at this note
Note 443867 - ORA-12154 Collective SAP note
Regards,
Cristian