I'm trying to build a superfilter (a simple hopper-backpack-hopper-backpack), so I'm using the Output-Block function to keep the items of interest, while anything else keep being sifted.

However, using more than one Output-Block makes it so neither of the expected filtered items are retained, unless the same item is present in both filter upgrades, which defeats their purpose.

For example, in a backpack that's being hopped: Filter upgrade 1 Output-Block-Match Item A and B. Filter upgrade 2 Output-Block-Match Item A and C. Items B and C get hopped while item A stays.

I think it extends to the inception upgrade and subbackpack filters, where the mother backpack's filter override and vice-versa, but I'd like to elaborate on that in a new post, so I can figure out what's happening.

I'm playing on the modpack Dawncraft: Echoes of Legends for 1.18.2 (forge-40.2.17).

This is a great mod, the best of its kind, and it cures my need for hoarding. Thanks.

This is because there's an OR relation between filters and that doesn't make sense with block filters - in your case with the example of the door it looks at the first filter and finds out that the door can't be moved out so it looks at the seconds filter, finds out that the door can be moved out and so it gets moved out of the backpack. You could switch to allow filters and list out what can be output in which case you can use however many filters you want and don't need to repeat items.

But I discussed this in the past and believe it should be doable to switch to AND relation if all the filters are set to block so I will leave this open as an enhancement to include that.