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

```
txSum += txCtAvg[j];
    }
    if (foundAnswer && txSum != 0) {
        txSum = txSum / 2;
        for (unsigned int j = minBucket; j <= maxBucket; j++) {
            if (txCtAvg[j] < txSum)
                txSum -= txCtAvg[j];
            else { 
                median = m_feerate_avg[j] / txCtAvg[j];
                break;
            }
        }
        passBucket.start = minBucket ? buckets[minBucket-1] : 0;
        passBucket.end = buckets[maxBucket];
    }
    
    if (passing && !newBucketRange) {
        unsigned int failMinBucket = std::min(curNearBucket, curFarBucket);
        unsigned int failMaxBucket = std::max(curNearBucket, curFarBucket);
        failBucket.start = failMinBucket ? buckets[failMinBucket - 1] : 0;
        failBucket.end = buckets[failMaxBucket];
        failBucket.withinTarget = nConf;
        failBucket.totalConfirmed = totalNum;
        failBucket.inMempool = extraNum;
        failBucket.leftMempool = failNum;
    }
    float passed_within_target_perc = 0.0;
    float failed_within_target_perc = 0.0;
    if ((passBucket.totalConfirmed + passBucket.inMempool + passBucket.leftMempool)) {
        passed_within_target_perc = 100 * passBucket.withinTarget / (passBucket.totalConfirmed + passBucket.inMempool + passBucket.leftMempool);