Funding
On perpetual futures a settlement between longs and shorts happens every few hours. An extreme rate means the crowd is heavily loaded on one side, and that often precedes a reversal.
The filter applies to crypto pairs only: forex has no funding, and the service will not let you enable it there.
News
Rejects signals around important releases: N minutes before and after. At such moments the usual regularities do not hold — the move is decided by a number in a report, not by the structure of the chart.
Spread
The difference between the buy and sell price. At rollover and on news the spread widens several times over, and a trade is losing before it opens. The filter drops signals when the spread is above a set value.
Correlation
Prevents several strongly related positions from being open at once. EURUSD and GBPUSD move alike; two signals on them are essentially one bet at double size.
Why they are sometimes "not applied"
All four need data that may not exist for a historical period: funding rates, a news calendar, spread quotes. When the data is missing, the filter is honestly marked as not applied — with the note "no data for the period".
This limitation is temporary: once the data appears, the filter works with no change to the configuration. That is exactly why the mark differs from the one on the adaptive threshold.