Running on recent master, commit f1dbf92ff0475a01d20170ea422c1d086acbbc57

If I run:
```
test/functional/feature_fee_estimation.py --randomseed 108574360997204915
```

I get:
```
2020-12-19T20:14:06.175000Z TestFramework (INFO): Initializing test directory /tmp/bitcoin_func_test_bcwexp78
2020-12-19T20:14:07.738000Z TestFramework (INFO): This test is time consuming, please be patient
2020-12-19T20:14:07.738000Z TestFramework (INFO): Splitting inputs so we can generate tx's
2020-12-19T20:14:10.870000Z TestFramework (INFO): Finished splitting
2020-12-19T20:14:12.104000Z TestFramework (INFO): Will output estimates for 1/2/3/6/15/25 blocks
2020-12-19T20:14:12.104000Z TestFramework (INFO): Creating transactions and mining them with a block size that can't keep up
2020-12-19T20:14:15.879000Z TestFramework (INFO): Creating transactions and mining them at a block size that is just big enough
2020-12-19T20:14:21.104000Z TestFramework (ERROR): Assertion failed
Traceback (most recent call last):
  File "/home/sdaftuar/ccl-bitcoin/2020-12-latest-master/test/functional/test_framework/test_framework.py", line 126, in main
    self.run_test()
  File "test/functional/feature_fee_estimation.py", line 256, in run_test
    check_estimates(self.nodes[1], self.fees_per_kb)
  File "test/functional/feature_fee_estimation.py", line 140, in check_estimates
    check_smart_estimates(node, fees_seen)
  File "test/functional/feature_fee_estimation.py", line 130, in check_smart_estimates
    % (feerate, last_feerate))
AssertionError: Estimated fee (0.000565) larger than last fee (0.000479) for lower number of confirms

```
{
    double estimate = -1;
    EstimationResult tempResult;
    if (doubleTarget <= shortStats->GetMaxConfirms()) {
        estimate = feeStats->EstimateMedianVal(doubleTarget, SUFFICIENT_FEETXS, DOUBLE_SUCCESS_PCT, nBestSeenHeight, result);
    }
    if (doubleTarget <= feeStats->GetMaxConfirms()) {
        double longEstimate = longStats->EstimateMedianVal(doubleTarget, SUFFICIENT_FEETXS, DOUBLE_SUCCESS_PCT, nBestSeenHeight, &tempResult);
        if (longEstimate > estimate) {
            estimate = longEstimate;
            if (result) *result = tempResult;
        }
    }
    return estimate;
}
/** estimateSmartFee returns the max of the feerates calculated with a 60%
 * threshold required at target / 2, an 85% threshold required at target and a
 * 95% threshold required at 2 * target.  Each calculation is performed at the
 * shortest time horizon which tracks the required target.  Conservative
 * estimates, however, required the 95% threshold at 2 * target be met for any
 * longer time horizons also.
 */
CFeeRate CBlockPolicyEstimator::estimateSmartFee(int confTarget, FeeCalculation *feeCalc, bool conservative) const