Sometimes it happens when few user process/program/transactions utilized maximum all SM12 lock entry, which may lead temporary bottle neck in system.
Also, its lead to ABAP dump of LOCK_TABLE_OVERFLOW in many situations.
Note: ** The size of the lock table limits the maximum number of lock entries, the maximum number of elementary lock names, and the maximum number of lock owners. In the case of an overflow of the lock table, you should check whether the update server is working correctly, since the lock table can grow very quickly if updates stop. If no update problems exist, you can use this parameter to increase the size of the lock table.
So, to check which user is culprit or responsible, which leads to this table overflow situation.
Go to SM12 –> click on Extra –> Top capacity used –> Current as shown below
Then it will show result like below, in which we can determine user list and no if lock occupied
Then we can identify the program/transaction run by user and ask them to cancel or we can cancel after proper communication.
Once it cancelled, system will back to normal.
To avoid such situation in future we can ask ABAPer to optimize the program or increase the allocated lock value through parameter enque/table_size after all the required approval.