ORA-00600: internal error code, arguments: [ktuUnReasonableScn]

 Problem:

On a 19c Active dataguard DB I started to see the following internal error in the alertlog:

ORA-00600: internal error code, arguments: [ktuUnReasonableScn], [10600], [6618907808447], [ktbgcl1], [3068], [], [], [], [], [], [], []
 

Analysis:

Searching MOS shows Bug 21147908 which is associated with Indexes creates on a Global Temporary Table GTT, in some cases the bug fix patch doesn't fix the bug completely! And they suggest dropping the indexes associated with the GTT.

Solution:

When checking the DB, I figured that the TEMPORARY tablespace on the ADG DB is almost full, I resolved that issue by just adding more tempfiles to the TEMPORARY tablespace on the ADG DB.