On my RAC system , port 8080 does not open after the reboot of the machine. The listener endpoint for APEX is lost.
All that needs to be done to re-establish the dropped listener endpoint for APEX is to toggle the APEX port using EXEC DBMS_XDB.SETHTTPPORT to a free port, then back to the defined port.
SQL> EXEC DBMS_XDB.SETHTTPPORT(8090); <– Pick any available port
SQL> EXEC DBMS_XDB.SETHTTPPORT(8080); <– Return to the established APEX port
netstat -an | grep 8080 will show that APEX has returned.
I haven’t try it on non-RAC systems.