How to fix my custom loot filter

I’ve made a very permissive loot filter for lvling on Filterblade.
However it hid too much, especially small rare items like 1h-swords.
So I added yet another class-based rule:
Show all items of rarity Rare or higher.
Small yellow items are now showing as expected.
However, random white items are also showing!
This only happens in-game, using FilterBlade’s simulation, they are hidden.

I don’t understand how this is possible since the rule specifies a Rarity of Rare or greater.

Another issue I have is easy testing of a rule for a specific item.
Often I want to change a rule based on a specific item being shown/hidden in game.
However when I run the simuation it can take a long time for an item with those parameters to drop.
So I end up having to load the filter in game.

I’ve watched NeverSink’s expert guide on FilterBlade.
But it seems I’m still missing details on how to use it.

I realize Path of Exile throws an error when trying to load the filter.
So it probably just rejects the use of a filter at all, showing everything.
The error is:
Unable to parse parameter for Class rule: No item classes matching “Flask”.
I’ve tried to fix this by manually editing the file and found the following setting at the end of the file:

Show # minimize junk instead of hiding (if "show")
Class "Amulets" "Belts" "Body Armour" "Boots" "Bows" "Claws" "Daggers" "Flask" "Gloves" "Helmets" "Jewel" "One Hand" "Quivers" "Rings" "Rune Dagger" "Sceptre" "Shields" "Staves" "Two Hand" "Wand" "Warstaff"
SetFontSize 18

So I tried changing “Flask” to “Flasks” and removing the item completely.
This has not helped, so there must be another instance.
I’ve also tried ploughing through the settings at FilterBlade, no luck.

Edit: I re-created a new high level filter from a FilterBlade basis, same problem. So I didn’t accidentally enter an invalid value.

Edit2: For some reason an older filter of mine does still work. I’ve tried to compare it to my newest filter but cannot find anything that might cause this problem.