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

```
void Write(AutoFile& fileout) const;
    /**
     * Read saved state of estimation data from a file and replace all internal data structures and
     * variables with this state.
     */
    void Read(AutoFile& filein, int nFileVersion, size_t numBuckets);
};
TxConfirmStats::TxConfirmStats(const std::vector<double>& defaultBuckets,
                                const std::map<double, unsigned int>& defaultBucketMap,
                               unsigned int maxPeriods, double _decay, unsigned int _scale)
    : buckets(defaultBuckets), bucketMap(defaultBucketMap), decay(_decay), scale(_scale)
{
    assert(_scale != 0 && "_scale must be non-zero");
    confAvg.resize(maxPeriods);
    failAvg.resize(maxPeriods);
    for (unsigned int i = 0; i < maxPeriods; i++) {
        confAvg[i].resize(buckets.size());
        failAvg[i].resize(buckets.size());
    }
    txCtAvg.resize(buckets.size());
    m_feerate_avg.resize(buckets.size());
    resizeInMemoryCounters(buckets.size());
}
void TxConfirmStats::resizeInMemoryCounters(size_t newbuckets) {