If after a reindex and tune still having the issue Found out sometimes rebuilding the control files can fix some issues. Apparently Rebuild Control files doesn’t just rebuild control files. But also rebuilds the redo logs, and checks the integrity of some other table and fixes issues within them.
To DO rebuild control files.
FIrst make a cold backup, or a backup of the database. ((very important since if rebuild control files goes sideways there is likely no coming back from it))
Then go into Techtoolkit and then control files and click on rebuild on the side.