Thank you for sharing your feedback regarding this but I wanted to chime in to help clarify your original inquiry and that it is increased chance.
So 40% increased chance for 1h sword prophecies, means that you’ll see around 40% more sword prophecies than before, not that you’ll see 1h sword prophecies an additional 40% of the time.
Hopefully, this helps. 
So if you can say, does this mean you have 40%per level for each new refilled prophecies to be swords or a 40%per level to have at least one sword prophecy to show up.
Myself personally I read it as each prophecy with have an increased odd to be the lens targeted item type.
I will note a few times I got like 5-6 1hd sword prophecies after a reroll. Issue was the odds seemed more in the favour to end up with no swords vs my desired outcome of more sword prophecies to pick from. It may be a case of reads one way means another.
That is what I pointed out in my initial post with the butchered math. But the math still doesn’t quite add up. Having 480% increased chance (40% per rank) the odds of getting the type you have in the lens should be somewhat close to 50%.
So failing to get one all those times in a row is a very very low statistical probablility.
Which means the formula behind this is not what we’re assuming it is. Can you shed some light on this, please? I’m genuinely curious because I’m a bit of a math nerd at times. 
Which is really the problem right now, when you Reroll 6-10 times straight and get absolutely no prophecies that match the lens you are using (of any rarity). This is why I pointed it out in my report a long time ago, which apparently went nowhere.
That’s why I asked how it works currently, because it could be just a case of the formula being used making it so that the odds don’t actually increase that much.
If the lens only increases you to something like 15%, for example, then the observed behaviour isn’t outside the norm. And if that’s the case, it’s a flawed design, rather than a bug.
Although they can apparently stack, so maybe this is implemented in a way where having 3 of them don’t simply roll only prophecies of that type and still have a decent chance of spawning other types? That seems to me to be the most likely reason.
I don’t think this will be changed during this season, given that the next one will have a CoF rework. And next season this might not even be applicable. But I’m curious to know how this was implemented, how the calculations are made for increased chance and whether or not it’s a bug.
I get the devs need to keep big changes for big content drops (season release) for a bigger chance of seasonal “success”, but that doesn’t mean (to me) that they can’t fix broken/underwhelming existing content with a “bandaid temp fix”.
Some bandaids to me could be: item type icon replacement, show favour cost for ez-er rerolling, remove auto reroll, add a reroll button hotkey(controller already has this).