ORA-01102: cannot mount database in EXCLUSIVE mode

One of the RAC instance is up, but the rest RAC instances failed to start up.

$sqlplus / as sysdba
SQL> startup;
ERROR at line 1:
ORA-01102: cannot mount database in EXCLUSIVE mode

.....
..
.
2025-02-18T13:46:48.148505+11:00
Error: Shutdown in progress. Error: 1102.
USER (ospid: 90061): terminating the instance due to ORA error 1102
2025-02-18T13:46:49.188764+11:00
Instance terminated by USER, pid = 90061