Re: Plan Baseline

Then there's the line

    SPM: couldn't reproduce any enabled+accepted plan so using the cost-based plan, planId = 460841780
So clearly Oracle tried using your baseline, but didn't get the same plan hash value as before.

Then you might recall an earlier post of mine saying: *In particular the one that leap to mind is the fact that you have several MERGE() hints in the outline - and there's an enhancement in 12.2.0.1 which deals with the problem that SPB's that contain MERGE() hints don't always reproduce the same plan because they don't specify what they merge into, only what they merge from. The unambiguous 12.2. syntax looks like: merge(_at_qb1 > qb2), e.g. merge(_at_SEL$12 > SEL$641071AC). So it's possible that with some change in estimated numbers the optimizer has merged query blocks in a different order - getting to the same final query block - and failed to reproduce the plan. *

Did you try searching MOS for details about that enhancement, or about a bug where SPM plans didn't always reproduced with merge() hints. If you had you might have found:
Bug 22542281 - MERGE hint syntax not explicit enough / syntax extended (Doc ID 22542281.8)
and then followed the patch link to find that there are several patches relating to 12.1.0.2 - so maybe you could patch your Oracle and get the SPB working.

Finally - a little creative speculation - maybe when Oracle tries to apply the baseline the initial "ignore_optim_embedded_hints" makes it ignore the cardinality hint, so the plan that appears is affected by the sampled content of the collection. IF (note the IF) that's the case then could you bypass the problem by using the sql_patch to add the cardinality (opt_estimate) hint until you've had a chance to test the patch for the known defect.