The following options address the solution:
1. (Tested) I assume that once the cold backup finished, it doesn't make sense to maintain the DB as RESTRICTED, so your DBA could set it ALLOWED:
SQL> alter system disable restricted session;
System altered.
SQL> SELECT logins from v$instance;
LOGINS
----------
ALLOWED
2. (Not Tested). Connecting to Oracle Instances Running in Restricted Mode
An Oracle instance can run in restricted mode, which allows access only to users who have the RESTRICTED SESSION system privilege.
To connect to an instance running in restricted mode, add the UR = A clause to the CONNECT_DATA parameter of the tnsnames.ora file as shown.
...
(CONNECT_DATA=
(SERVICE_NAME = acct.us.yourcompany.com)
(UR = A)
)
3. (Tested and works). KB 261629: How automatically reconnect Stat Central Agent after DB closed connection?
On the SCA machine, open with an editor the file standalone-full.xml located under $STAT_HOME/app/standalone/configuration and search for the keyword "SYSTEM_TBL".
<validation>
<check-valid-connection-sql>SELECT STAT_DB_VERSION FROM SYSTEM_TBL</check-valid-connection-sql>
<validate-on-match>false</validate-on-match>
<background-validation>true</background-validation> <-- add this line
<background-validation-millis>200000</background-validation-millis> <-- add this line
</validation>
