I reinstalled the app, same thing.
I didn’t expect it to fix anything because I already reinstalled to get rid of the tool delay recently.
This is on a 2nd gen ipad pro 12.9”

https://litter.catbox.moe/0qq1ij.MOV
here is a video showing a fresh install producing the same effect

A basic smudge brush darkening a solid colour for literally no reason is entirely an app issue, and the pigment group smudge brushes exhibit the same behaviour because again, the fundamental interaction between the smudge tool and pigment layer is really bad
The engine has a lot of issues even outside the context, and I made multiple threads reporting these

I’ve had negligible delay when switching tools, but I’m suddenly having pretty bad delay when colorpicking with the tap gesture (which I guess is technically switching tools), around a second, maybe even 2 between colorpicking and being able to paint again

Edit: Well, as uterr above mentioned, reinstalling seems to have fixed it, but I now need to change all the settings back and the brushes are gone so I had to export everything. Files aren’t lost, it seems.

The pattern opacity dynamic setting doesn’t do anything unless the pattern is set to blend each stamp. Manually changing pattern opacity produces an effect on the stroke either way, so it seems there’s a bug related to the dynamic setting.

Hi, I think this might be an oversight: the wet paint/smudge tool doesn’t seem to sample on the first stamp with the flat setting, only after the number of stamps mix rate is set to. In the image attached at the top, you can see the wet brush only sampling after 19 stamps, the initial 19 being in the selected colour, unaffected by wetness settings or underlying colours. On the bottom, the smudge tool set to flat and a mix rate of 5 was dragged over the blue stroke, but only started doing anything after 5 stamps, thus ignoring blue and only picking up the 5th red stamp. Above it you can see the same brush with blur disabled working as expected from the first stamp.

Edit:
Another thing I just noticed is that full blend transparency might not be working as intended.
Namely, it behaves very differently with set opacity than with that same opacity achieved via pressure.
In the image, the top is what I’d expect to happen when sampling only the current layer, transparency of the opaque pixels is affected only when “dragged in” from the outside, as if transparency was a different colour, like the blue on the right of it. Both of these have the opacity set to 50%, and you can see the transparency is applied. Both of these also have minimum opacity in the dynamics panel set to 100%, though disabling opacity dynamics achieves the same result.
However, if the opacity dynamic is enabled and the minimum opacity setting set to below 100%, the smudge will set every pixel it touches to the opacity achieved by the pressure regardless of any other factor, like an a brush using the clear blending mode, only in reverse (ie where a brush using clear and 10% opacity would apply 10% transparency to the pixel, a smudge with full blend and current layer would SET the opacity of the pixel to 10%, but only if the opacity was above 10%).
In the image on the bottom is an example, smudge set to full blend transparency and minimum opacity of 50%, with the opacity dynamics enabled and using minimal pressure to get that 50% opacity, you can see it just sets the opacity to 50% even though there are no transparent pixels to inherit the transparency from.

I know this might be confusing to read, but if you make a new layer, fill it with any colour, set the smudge to full transparency and sampling the current layer, turn on opacity dynamics with minimum opacity set to let’s say 0% and apply that to the solid colour filled layer, you will see it acting almost like an eraser.
Now if you take the same brush, but disable opacity dynamics and set the opacity manually with the opacity slider, you will see it acting completely differently, as it will no longer act like an eraser even though there should be no mechanical difference.

Also, I’d again like to point out that the wetness settings are only accessible through brush settings, needing a minimum of 3 taps to access, and 4 if the brush is in the favourites menu, as you need to tap open the brush panel > … > edit this brush > wetness.
The settings cannot be found in the tool option panel, cannot be added to the side sliders, nor can “edit this brush” be added to the quick menu or the taskbar.
If you look at photoshop, you’ll see the relevant sliders at the top of the screen when using the equivalent tools. I understand screen economy is much stricter on an ipad, but there’s still the need to access these settings, perhaps a toggle to replace the flow/opacity slider with wetness when using the tools, like there is a 1px spacing toggle for the smudge tool, or adding the settings to the tool option panel when using the tools, like how sampling already is.
Spacing and softness are good candidates to be added to the tool panel as well, imo

sigh, i guess ill report the bug if i lose a file due to this new saving method. I'm just EXTREMELLY paranoid about apps corrupting files, infinite painter did and still does corrupt files due to its poorly implemented saving function... dunno whats that developer even doing, file corruption has been in his app since release and happens quite often...

as someone who did ask for the procreate saving system, artstudio’s system is better because of the version history feature, which I’m told isn’t possible the way procreate does things
I never had a corrupted file with artstudio, but even if I did, I could just reload the previous version

I haven’t read the whole discussion, but regarding the “nudge mode”, is that not already achieved by toggling “snappable sliders” off?

Would it be possible to make the smudge/wet brush not sample pixels outside the selection? Right now selection only limits where new pixels can be placed, I think it would be more useful if selection could be used to protect the intended area of effect from adjacent colours.
Here’s an image to illustrate what I mean, left is what happens when the tool is set to sample the current layer only, the tool doesn’t let the white of the background onto the layer, which is what I’d expect when selecting an area that smudge affects.
Right is what happens when with a selection and the smudge sampling all layers, the white of the background leaks in.
Middle has the green on the same layer and smudge sampling the current layer, the green leaks in.
This leads to muddy colours when trying to blend tightly placed tiles and sort of defeats the purpose of the smudge tool for m due to needing to erase and manually correct a lot of areas.