I recently faced this issue in our production ENV.
After doing a SwitchOver from Production to replica, Replica was facing frequent ORA-01555 error for lots of the Read only Queries.
After Investigation found below error in alert log
ORA-01555 / ORA-600 [ktbdchk1: bad dscn] / ktbGetDependentScn / Dependent scn violations as the block ITL has higher COMMIT SCN than block SCN
This is a Oracle bug in 11.2 as per the oracle doc.
Bug 22241601 ORA-600 [kdsgrp1] / ORA-1555 / ORA-600 [ktbdchk1: bad dscn] / ORA-600 [2663] due to Invalid Commit SCN in INDEX ( Doc ID 1608167.1 ).
As a solution had to set below parameter on Production and replica both.
alter
system set "_ktb_debug_flags"=8;
didn't faced Problem after using this parameter :)
