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

```
newBucketRange = false;
        }
        curFarBucket = bucket;
        nConf += confAvg[periodTarget - 1][bucket];
        totalNum += txCtAvg[bucket];
        failNum += failAvg[periodTarget - 1][bucket];
        for (unsigned int confct = confTarget; confct < GetMaxConfirms(); confct++)
            extraNum += unconfTxs[(nBlockHeight - confct) % bins][bucket];
        extraNum += oldUnconfTxs[bucket];
        
        
        
        
        if (totalNum >= sufficientTxVal / (1 - decay)) {
            double curPct = nConf / (totalNum + failNum + extraNum);
            
            if (curPct < successBreakPoint) {
                if (passing == true) {
                    
                    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;
                    passing = false;
                }
                continue;