Yes, indeed, they are low because in ~10 minutes after a fee rate estimate, if there is a high inflow of transactions, there is a likelihood of transactions getting bumped out by other transactions with higher mining scores. If you estimated the fee rate with the 50th percentile of the block weight, and the weight of new transactions in the mempool with higher mining scores is > 4000000/2, then it’s most likely that your transaction will be bumped out and will not be mined in the next block.
You would have to make a new fee rate estimate and RBF bump the transaction in this case.
We could also use the top 25th percentile to reduce the likelihood of getting bumped out; and also reduce the low estimates.
Yes I think it will lower the fee rate estimate! and the potential of getting bumped out is higher in this case.
In this case, the sanity checks will indicate that we are not in sync with miners and we will not use this estimation mode, we could just fall back to CBlockPolicyEstimator?