It is difficult for fee estimators to accurately predict the minimum required fee because the time until the next block is always unknown. If a block was just found, the mempool will have fewer high-paying transactions, but it is reasonable to expect that high-paying transactions will appear in the mempool over time until the next block is found. This makes estimating the required fee difficult because you don't know when the next block will be found, and in cases when a lot of mining capacity is being taken on/offline, the fee estimator may not even know how long until the expected time of the next block.

A lot of posts in this thread, and in posts in other, similar threads talk about the required fee to get a single transaction confirmed, but this fee rate would probably not be appropriate if you need 50, 100, or more transactions confirmed in nearly every block, as many larger bitcoin businesses may need. A large business who pays the minimum required fee might get a portion of their transactions confirmed quickly, but would quickly see their transactions pile up as being unconfirmed, which will cause problems. I think a business that consistently needs many transactions confirmed in every block would need to pay something closer to the median fee rate. This has the potential to cause confusion to some of the fee estimators out there.