Hello Debby,
Hope you are doing good.
We too have recently upgraded our database to 12c and since then our queries just keep running and we need to eventually kill the running query. It neither gives any error.
We were informed that we should update the Oracle client also to 12c which we have done but we have ended up unsuccessful.
Hence, we are really not able to understand if this is an issue on TOAD or ORACLE.
Appreciate any help from you on this regard.
Thanks,
Sachin